Successive Si-H/Si-C bond cleavage of tertiary silanes on diruthenium centers. Reactivities and fluxional behavior of the bis(μ-silylene) complexes containing μ-hydride ligands

Organometallics 2003, 22, 3855-3876

3855

Su ccessive Si-H/Si-C Bon d Clea va ge of Ter tia r y Sila n es

on Dir u th en iu m Cen ter s. Rea ctivities a n d F lu xion a l

Beh a vior of th e Bis(µ-silylen e) Com p lexes Con ta in in g

µ-Hyd r id e Liga n d s^†

Toshiro Takao, Masa-aki Amako, and Hiroharu Suzuki*

Department of Applied Chemistry, Graduate School of Science and Engineering,

Tokyo Institute of Technology, and CREST, J apan Science and Technology Corporation (J ST),

2-12-1 O-okayama, Meguro-Ku, Tokyo 152-8552, J apan

Received J une 3, 2003

A series of µ-silylene complexes was synthesized by way of sequential Si-H and Si-C

bond scission of tertiary silanes on diruthenium centers generated from Cp*Ru(µ-H)₄RuCp*

(1; Cp* ) η⁵-C₅Me₅). While both bis- and mono(µ-diphenylsilylene) complexes, {Cp*Ru(µ-

SiPh₂)(µ-H)}₂(3a ) and {Cp*Ru(µ-H)}₂(µ-SiPh₂) (4a ), were obtained in the case of Ph₃SiH,

the reactions of 1 with Ph₂MeSiH and PhMe₂SiH exclusively afforded bis(µ-silylene)

complexes, {Cp*Ru(µ-SiPhMe)(µ-H)} (3b-syn /a n ti) and {Cp*Ru(µ-H)}₂(µ-SiPhMe)(µ-SiMe₂)

(3c), respectively. The Si-C bond scission proceeded via prior π-coordination of the phenyl

group of the intermediary formed silyl groups, which was supported by the fact that the

reaction of 1 with (CH₂dCH)RSiH₂(R ) Ph, Me) afforded exclusively the mono(µ-silylene)

complex {Cp*Ru(µ-H)}₂(µ-SiEtR) (4b, R ) Me; 4c, R ) Ph) as a result of intramolecular

coordination of the vinyl group. Reaction of a mixture of 3b-syn and 3b-a n ti with PMe₃

afforded the bis(µ-silylene) complex {Cp*Ru(µ-SiPhMe)}₂(PMe₃)(H)₂(5), which adopted only

the syn structure with respect to the two bridging silylene ligands. Isomerization of the

anti to the syn form arose from rotation of the bridging silylene ligands, which was confirmed

by the VT-NMR studies of 3b-syn and 3c. While reactions of 3 with H₂and CO afforded

respectively the bis(µ-silyl) complexes {Cp*Ru(µ-η²-HSiR₂)}₂(µ-H)(H) (2) and bis(µ-silylene)

complexes containing two terminal carbonyl groups {Cp*Ru(CO)(µ-SiR₂)}₂(6), liberation of

the bridging silylene ligand of 4 was observed during the reaction with H₂and CO, together

with formation of the mono(µ-silylene) complex {Cp*Ru(CO)}(µ-CO)(µ-SiR¹R²) (8a , R¹) R²

) Ph; 8b, R¹) Me, R²) Et; 8c, R¹) Ph, R²) Et). X-ray diffraction studies were performed

on 3c, 4a ,b, 5, and 8a ,b, and they clearly demonstrated the bridging silylene structures of

these complexes.

In tr od u ction

silane, silyl, silylene, silylyne, silene, and disilene

complexes are known.⁴

Reaction of organosilicon compounds with transition-

metal complexes has been widely investigated in rela-

tion to silane polymerization,¹hydrosilylation,²and

redistribution at the silicon.³Complexes obtained by

oxidative addition of an Si-H bond are very important

because they are considered to be key intermediates of

such catalytic reactions. Many kinds of complexes

having silicon ligands thus have been synthesized,

which also revealed the ability of the silicon atom to

attach to a metal center in various modes; for example,

Among these categories, µ-silylene or µ-silyl com-

plexes that have a bridging silicon ligand are one of the

most widely investigated classes of silicon complexes.⁵

Reaction of a primary and a secondary silane with a

mononuclear complex often afforded a dimeric product

by successive oxidative addition of two Si-H bonds. For

example, the monomeric manganese complex (η⁵-C₅-

Me₅)Mn(CO)₃reacts with SiH₄upon irradiation to

generate the dimanganese complex {(η⁵-C₅Me₅)Mn(CO)-

(H)}₂(µ-SiH₂).⁶In this reaction, two Si-H bonds act as

^†Dedicated with admiration and appreciation to Professor Akio

Yamamoto and Dr. Nobuhiro Tamura, Technical director of the CREST

project.

(1) Gauvin, F.; Harrod, J . F.; Woo, H.-G. Adv. Organomet. Chem.

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Tanaka, M. Chem. Lett. 1988, 1411-1414.

(4) For example: (a) Shubert, U. Adv. Organomet. Chem. 1990, 30,

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Organomet. Chem. 1973, 11, 253-330. (e) Tilley, T. D. In The

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Publication on Web 08/15/2003

3856 Organometallics, Vol. 22, No. 19, 2003

Takao et al.

Sch em e 1

Cooperative action of the two ruthenium atoms was

clearly represented in this reaction; one of the two

ruthenium nuclei acts as a coordination site, and the

other is an activation site. We will use the term

multimetallic activation to refer to a distinctive manner

of activation achieved by the concerted interaction

among substrates and multiple metal centers. Recently,

we reported another example of the bimetallic activation

using vinylsilanes as substrates, in which it was shown

that oxidative addition of an Si-C bond readily pro-

ceeded via formation of a µ-η²:η²-vinylsilane complex.^11b

Although an Si-C bond was thought to be inert toward

oxidative addition,¹²it was activated effectively by the

cooperative action of two adjacent metal nuclei on the

diruthenium system.

We describe herein a new example of bimetallic

activation involving successive Si-H/Si-C(aryl) and

Si-H/Si-C(sp³) bond cleavage. These reactions provided

a new synthetic method of µ-silylene complexes using

monohydrosilanes. Some reactions of the bis(µ-silylene)

complex {Cp*Ru(µ-SiR₂)(µ-H)}₂(3) and mono(µ-silylene)

complex {Cp*Ru(µ-H)}₂(µ-SiR₂) (4) with small molecules

are also mentioned. Both complexes have a bridging

divalent silicon ligand, and the structural data around

the silicon, Ru-Si-Ru angles and Ru-Si distances,

were similar to each other, but it was proved that their

chemical properties are quite different. While ²⁹Si

signals of mono(µ-silylene) complexes 4 appeared at a

low magnetic field region (ca. δ 280 ppm) that was

typical for a µ-silylene ligand,⁵those of bis(µ-silylene)

complexes 3 were observed at a considerably higher field

region as the µ-silylene ligand (ca. δ 110 ppm). This

implies that the bonding interaction between ruthenium

and silicon is quite different in each compound, and this

difference was reflected in the reactivities with small

reactive molecules.

a clamp to bind two metal nuclei by oxidative addition.

It has also been shown that reaction of a dinuclear

complex with a secondary silane resulted in the forma-

tion of a bridging silicon ligand.^7,8

Thus far, many µ-silyl/silylene complexes have been

synthesized in these ways, but most of them were

studied only from an inorganic chemistry point of view.

Although numerous structurally characterized com-

plexes having a bridging silicon ligand are known, only

quite limited studies of the reactivity have been

done.^8b,c,9,11We previously reported that the bis(µ-silyl)

complexes {Cp*Ru(µ-η²-HSiR₂)}₂(µ-H)(H) (2a , R ) Ph;

2e, R ) Et; Cp* ) η⁵-C₅Me₅) were obtained by the

reaction of the dinuclear ruthenium complex Cp*Ru(µ-

H)₄RuCp* (1) with R₂SiH₂(R ) Et, Ph) (Scheme 1).^7aIt

was revealed that two 2e-3c Ru-H-Si bonds were

formed in bis(µ-silyl) complexes. The 2e-3c M-H-Si

bond has been considered to be a frozen intermediate

of the oxidative addition of an Si-H bond.^4a,10Actually,

η²-coordinated Si-H bonds of 2a underwent an oxida-

tive addition reaction upon heating to yield the bis(µ-

silylene) complex {Cp*Ru(µ-SiPh₂)(µ-H)}₂(3a ).^7a

Resu lts a n d Discu ssion

Rea ction of Cp *Ru (µ-H)₄Ru Cp * (1) w ith P h ₃SiH.

Reaction of the diruthenium tetrahydride complex

Cp*Ru(µ-H)₄RuCp* (1) with triphenylsilane yielded a

mixture of the bis(µ-diphenylsilylene) complex {Cp*Ru-

(µ-SiPh₂)(µ-H)}₂(3a ) and the mono(µ-diphenylsilylene)

complex {Cp*Ru(µ-H)}₂(µ-SiPh₂) (4a ) (eq 1). The ratio

between 3a and 4a was dependent on the reaction

conditions. Treatment of 1 with small excess amounts

(7) (a) Suzuki, H.; Takao, T.; Tanaka, M.; Moro-oka, Y. J . Chem.

Soc., Chem. Commun. 1992, 476-478. (b) Takao, T.; Yoshida, S.; Suzki,

H.; Tanaka, M. Organometallics 1995, 14, 3855-3868. (c) Ohki, Y.;

Kojima, T.; Oshima, M.; Suzuki, H. Organometallics 2001, 20, 2654-

2656.

(8) (a) McDonald, R.; Cowie, M. Organometallics 1990, 9, 2468-

2478. (b) Wang, W.-D.; Eisenberg, R. J . Am. Chem. Soc. 1990, 112,

1833-1841. (c) Wang, W.-D.; Eisenberg, R. Organometallics 1992, 11,

908-912. (d) Carren˜o, C.; Riera, V.; Ruiz, M. A.; J eannin, Y.; Philoche-

Levisalles, M. J . Chem. Soc., Chem. Commun. 1990, 15-17. (e) Fryzuk,

M. D.; Rosenberg, L.; Rettig, S. J . Organometallics 1991, 10, 2537-

2539. (f) Fryzuk, M. D.; Rosenberg, L.; Rettig, S. J . Inorg. Chim. Acta

1994, 222, 345-364. (g) Fryzuk, M. D.; Rosenberg, L.; Rettig, S. J .

Organometallics 1996, 15, 2871-2880. (h) Rosenberg, L.; Fryzuk, M.

D.; Rettig, S. J . Organometallics 1999, 18, 958-969. (i) Campion, B.

K.; Heyn, R. H.; Tilley, T. D. Organometallics 1992, 11, 3918-3920.

(j) Brittingham, K. A.; Gallaher, T. N.; Schreiner, S. Organometallics

1995, 14, 1070-1072. (k) Akita, M.; Hua, R.; Nakanishi, S.; Tanaka,

M.; Moro-oka, Y. Organometallics 1997, 16, 5572-5584. (l) Kayser,

B.; Eichberg, M. J .; Vollhardt, K. P. C. Organometallics 2000, 19,

2389-2392.

(9) (a) Corriu, R. J . P.; Moreau, J . J . E. J . Chem. Soc., Chem.

Commun. 1980, 278-279. (b) Carre´, F. H.; Moreau, J . J . E. Inorg.

Chem. 1982, 21, 3099-3105. (c) Horng, K. M.; Wang, S. L.; Liu, C. S.

Organometallics 1991, 10, 631-635. (d) Corriu, R. J . P.; Lanneau, G.

F.; Cjauhan, B. P. S. Organometallics 1993, 12, 2001-2003. (e) Wang,

W.-D.; Eisenberg, R. Organometallics 1991, 10, 2222-2227. (f) Hash-

imoto, H.; Hayashi, Y.; Aratani, I.; Kabuto, C.; Kira, M. Organome-

tallics 2002, 21, 1534-1536. (g) Hashimoto, H.; Aratani, I.; Kabuto,

C.; Kira, M. Organometallics 2003, 22, 2199-2201.

(10) Crabtree, R. H. Angew. Chem., Int. Ed. Engl. 1993, 32, 789-

805.

Bond Cleavage of Tertiary Silanes on Ru₂Centers

Organometallics, Vol. 22, No. 19, 2003 3857

F igu r e 2. Molecular structure of {Cp*Ru(µ-H)}₂(µ-SiPh₂)

(4a ), with thermal ellipsoids at the 30% probability level.

Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles

(d eg) for 4a

Ru(1)-Ru(2)

Ru(1)-Si(1)

Ru(2)-Si(1)

Si(1)-C(1)

Si(1)-C(7)

2.4686(5)

2.3498(12)

2.3436(11)

1.884(5)

Ru(1)-H(1)

Ru(1)-H(2)

Ru(2)-H(1)

Ru(2)-H(2)

1.86(5)

1.80(7)

1.83(5)

1.896(4)

F igu r e 1. Molecular structure of {Cp*Ru(µ-SiPh₂)(µ-H)}₂

(3a ), with thermal ellipsoids at the 30% probability level.

Ru(2)-Ru(1)-Si(1)

Ru(1)-Ru(2)-Si(1)

Ru(1)-Si(1)-Ru(2)

58.14(3)

58.39(3)

63.47(3)

H(1)-Ru(1)-H(2)

H(1)-Ru(2)-H(2)

C(1)-Si(1)-C(7)

81(3)

79(3)

108.6(2)

Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles

(d eg) for 3a

The solubility of both complexes, 3a and 4a , in organic

solvents was quite low; thus, it was difficult to separate

them as they were. While complex 3a reacts with 1 atm

of H₂at ambient temperature to yield the bis(µ-silyl)

complex 2a , which is very soluble in pentane, complex

4a does not react under those conditions. The mixture

was converted to a mixture of 2a and 4a on exposure to

1 atm of H₂. Complex 4a , then, was isolated in analyti-

cally pure form by rinsing with pentane. Complex 4a

was fully characterized on the basis of ¹H, ¹³C, and ²⁹Si

NMR, IR, and FD-MS spectral data as well as analytical

data. The structure of 4a was determined by X-ray

diffraction studies using a single crystal obtained from

a diluted cold CH₂Cl₂solution.

The molecular structure of 4a is shown in Figure 2,

which clearly demonstrates the dinuclear structure

bridged by a silicon atom. Hydride ligands bonded to

ruthenium atoms were located during sequential dif-

ference Fourier syntheses and were refined isotropically.

The crystal data for 4a are given in the Experimental

Section (Table 8), and selected bond lengths and angles

are given in Table 2.

Ru-Ru*

Ru-Si

2.665(0)

2.364(1)

2.360(1)

1.891(3)

Ru-H

1.72(3)

1.73(3)

1.885(2)

Ru-H*

Si-C(21)

Ru-Si*

Si-C(11)

Si-Ru-Si*

Ru-Si-Ru*

111.30(3)

68.80(3)

H-Ru-H*

C(11)-Si-C(21)

79(1)

107.2(1)

of Ph₃SiH (3.0 equiv) afforded a mixture, in which the

3a :4a ratio was estimated at 4:3. In contrast, when an

equimolar amount of Ph₃SiH is slowly added dropwise

to the solution of 1, the 3a :4a ratio changes to 1:5.

In the ¹H NMR spectrum of the mixture, two Cp*

signals were observed at δ 1.40 and 1.59. The former

signal was assignable to 3a , which was independently

synthesized by thermolysis of the bis(µ-diphenylsilyl)

complex {Cp*Ru(µ-η²-HSiPh₂)}₂(µ-H)(H) (2a ).^7aComplex

3a was already characterized and structurally deter-

mined by X-ray diffraction studies (Figure 1, Table 1).

A singlet resonance of the hydrides of 3a was observed

at δ -19.70. Such a high-field shift around δ -20 is

characteristic for the signal of hydride ligands of the

bis(µ-silylene) complexes 3.

The Ru(1)-Ru(2) distance, 2.4686(5) Å, was similar

to that of 1 (2.4630(5) Å)¹³and considerably shorter than

that of 3a (2.665(0) Å).^7aThe Ru-Ru distance of 2.46 Å

corresponds to that of a triple bond between two

The other Cp* signal observed at δ 1.59 was assign-

able to that of the mono(µ-diphenylsilylene) complex

{Cp*Ru(µ-H)}₂(µ-SiPh₂) (4a ). The signal of the hydrides

of 4a was found at δ -13.51 as a singlet.

(11) (a) Takao, T.; Suzuki, H.; Tanaka, M. Organometallics 1994,

13, 2554-2556. (b) Takao, T.; Amako, M.; Suzuki, H. Organometallics

2001, 20, 3406-3422.

(13) (a) Suzuki, H.; Omori, H.; Lee, D.-H.; Yoshida, Y.; Moro-oka,

Y. Organometallics 1988, 7, 2243-2245. (b) Suzuki, H.; Omori, H.; Lee,

D.-H.; Yoshida, Y.; Fukushima, M.; Tanaka, M.; Moro-oka, Y. Orga-

nometallics 1984, 13, 1129-1146.

(12) Sakaki, S.; Ieki, M. J . Am. Chem. Soc. 1993, 115, 2373-2381.

3858 Organometallics, Vol. 22, No. 19, 2003

Takao et al.

Sch em e 2^a

a

Ru ) (C₅Me₅)Ru.

ruthenium nuclei, and a triple bond makes each ruthe-

nium coordinatively saturated according to the EAN

rule. An ab initio MO calculation of 1, however, sug-

gested that there was no bonding interaction between

two ruthenium atoms.¹⁴It was concluded in this paper

that the Ru-Ru distance was shortened as a result of

ligation of the four hydrides in the bridging mode, which

bound two ruthenium nuclei strongly. Though concrete

evidence for an Ru-Ru bonding interaction is lacking

at present, the very acute Ru(1)-Si-Ru(2) angle

(63.49(4)°) implies that there would be a strong interac-

tion between two ruthenium atoms.¹⁵

appeared in a very wide range (δ 59.5-289.1).⁵In this

case, however, since both 3a and 4a have the same

substituents on the bridging silicon and their Ru-Si

σ-bond distances were nearly the same, the chemical

shift of the ²⁹Si NMR spectra probably reflects the

difference in their bonding interaction, which is dis-

cussed later.

It is obvious that the µ-silylene complexes 3a and 4a

were formed as a result of Si-C(aryl) bond cleavage of

Ph₃SiH. The phenyl group was eliminated as benzene,

and generation of benzene was confirmed by means of

GC-MS. Neither biphenyl nor diphenylsilane was formed.

Such Si-C(aryl) bond cleavage would be achieved by

the concerted interaction of the two adjacent ruthenium

atoms. The reaction was monitored by means of ¹H

NMR, but no detectable intermediate was observed

during the reaction. Generation of dihydrogen was

confirmed by the singlet observed at δ 4.51. Akita et al.

also reported Si-C(aryl) bond cleavage by the reaction

of the diruthenium complex {CpRu(µ-CH₂)}₂(CO)(MeCN)

(Cp ) η⁵-C₅H₅) with Ph₃SiH to yield a µ-silylene

complex.^8kThe Si-C(aryl) bond cleavage of triphenyl-

silane most likely proceeds via formation of the µ-tri-

phenylsilane intermediates B and E shown in Scheme

2. Intramolecular coordination of a vinyl group of a

dimethylvinylsilane in the µ-η²:η²-dimethylvinylsilane

complex {Cp*Ru(µ-H)}₂{µ-η²:η²-HSiMe₂(CHdCH₂)} was

confirmed by means of the X-ray diffraction studies,

which can be regarded as a model compound of inter-

mediate B in Scheme 2.^11bA P-C bond of PPh₃was also

cleaved by the tetrahydride complex 1 at ambient

temperature, which afforded the µ-phosphido complex

(Cp*Ru)₂(µ-PPh₂)(µ-η²:η²-C₆H₆)(µ-H).¹⁷

The Ru-Si distances (2.3498(12), 2.3436(11) Å) lie in

the range of the reported values for Ru-Si σ-bond

lengths (2.288(11)-2.507(8) Å)^4band were nearly equal

to those of 3a (average 2.36 Å). Although there was no

distinct difference in the Ru-Si distances between 3a

and 4a , their magnetic environment was proved to be

considerably different by means of ²⁹Si NMR spectros-

copy. The ²⁹Si signals of 3a and 4a appeared at δ 109.8

and 265.0, respectively. It has been noted that the

chemical shift of a silicon ligand depends on various

factors, such as electron negativity of the substituent,

coordination number, p_π-d_πand, d_π-d_πinteractions,

and so on.¹⁶Thus, it seems to be difficult to predict the

coordination mode of a silicon atom only on the basis of

1

the chemical shift such as H and ¹³C NMR. Indeed , it

was known that ²⁹Si signals of µ-silyl/silylene complexes

(14) Koga, N.; Morokuma, K. J . Mol. Struct. 1993, 300, 181-189.

(15) (a) Coleman, J . M.; Dahl, L. F. J . Am. Chem. Soc. 1967, 89,

542-552. (b) Stevenson, D. L.; Dahl, L. F. J . Am. Chem. Soc. 1967,

89, 3721-3726. (c) Dahl, L. F.; De Gil, E. R.; Feltham, R. D. J . Am.

Chem. Soc. 1969, 91, 1653-1654. (d) Connelly, N. G.; Dahl, L. F. J .

Am. Chem. Soc. 1970, 92, 7470-7472. (e) Connelly, N. G.; Dahl, L. F.

J . Am. Chem. Soc. 1970, 92, 7472-7474.

(16) Williams, E. A. In The Chemistry of Organic Silicon Com-

pounds; Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1989; Chapter

8, pp 511-554.

(17) Omori, H.; Suzuki, H.; Take, Y.; Moro-oka, Y. Organometallics

1989, 8, 2270-2272.

Bond Cleavage of Tertiary Silanes on Ru₂Centers

Organometallics, Vol. 22, No. 19, 2003 3859

Complex 4a did not react with Ph₃SiH at ambient

temperature. This fact strongly indicates that bis(µ-

silylene) complex 3a was not produced via 4a , and it is

noteworthy that 3a and 4a were formed via independent

paths. Triphenylsilane is so large that coordination of

the second molecule of Ph₃SiH was suppressed by its

steric demand. Coordination of an Si-H bond of the

second molecule would compete with intramolecular

coordination of the phenyl group. Such suppression by

the intramolecular coordination is clearly seen in the

reaction of 1 with the secondary vinylsilane (CHdCH₂)-

RSiH₂(vide infra).

the exclusive formation of {Pt(PR₃)(µ-SiMe₂)(µ-H)}₂.¹⁸

J udging from these reactions, oxidative addition of an

Si-C(aryl) bond is more preferable than that of an Si-

C(sp³) bond. This preference was most likely due to the

ability of of the phenyl group to engage in η²coordina-

tion to the neighboring metal center, and η²coordination

would facilitate the Si-C(aryl) bond cleavage. Such

bond cleavage assisted by η²coordination of a phenyl

group has appeared in earlier papers.¹⁹

Although complexes 3b-syn and 3b-a n ti were not

separated from each other, they were characterized on

the basis of ¹H, ¹³C, and ²⁹Si NMR spectra and FD-MS

1

spectra of the mixture. In the H NMR spectra of the

Rea ction of Cp *Ru (µ-H)₄Ru Cp * w ith P h ₂MeSiH.

The reaction of 1 with 2 molar equiv of diphenylmeth-

ylsilane afforded a mixture of two diastereomers of the

bis(µ-silylene) complex {Cp*Ru(µ-SiPhMe)(µ-H)}₂(3b-

syn and 3b-a n ti) with respect to the orientation of the

substituents at the bridging silicons (eq 2). The ratio

mixture measured at -40 °C, three resonances for the

hydride ligands were observed. A singlet observed at δ

-20.44 was assignable to the hydride signal of 3b-a n ti,

and two doublets observed at δ -21.01 (J _H-H) 6.1 Hz)

and -19.77 (J _H-H) 6.1 Hz) were assignable to those of

3b-syn . Although the signals assignable to 3b-a n ti did

not show any broadening even in the higher tempera-

ture region, the hydride signals of 3b-syn coalesced into

one signal at 20 °C. However, the shape of Cp* and

methyl proton signals of 3b-syn did not change upon

warming. These results show that the site-exchange

process of the hydride ligands occurs in the bis(µ-

silylene) complexes. Activation parameters of this flux-

ional process were estimated at ∆H^q) 16.7 ( 0.4 kcal

mol^-1and ∆S^q) 12.5 ( 1.6 cal mol^-1K^-1. Mechanistic

studies of the fluxional processes are discussed in detail

later.

Although hydride signals of 3b-a n ti were not de-

pendent on temperature, the two hydride ligands in 3b-

a n ti likely exchange as those observed in 3b-syn . Since

3b-a n ti adopts a C₂-symmetrical structure with respect

to the Ru-Ru axis, two hydride ligands are always kept

in magnetic equivalence. Therefore, the site-exchange

process would not appear in the NMR signals of 3b -

a n ti. This feature is also applied to the bis(µ-diphenyl-

silylene) complex 3a , which has a D_2hstructure.

Rea ction of Cp *Ru (µ-H)₄Ru Cp * w ith P h Me₂SiH.

While Si-C(sp³) bond cleavage of Ph₂MeSiH was not

observed as mentioned above, Si-C(sp³) bond scission

of PhMe₂SiH occurred in the reaction of 1 with PhMe₂-

SiH. Treatment of 1 with 2 molar equiv of PhMe₂SiH

afforded a mixture of the mixed-bridge bis(µ-silylene)

complex {Cp*Ru(µ-H)}₂(µ-SiPhMe)(µ-SiMe₂) (3c) and

the bis(µ-silyl) complex (Cp*Ru)₂(µ-η²-HSiPhMe)(µ-η²-

HSiMe₂)(µ-H)(H) (2c). Small amounts of {Cp*Ru(µ-

SiMe₂)(µ-H)}₂(3d ) and {Cp*Ru(µ-η²-HSiMe₂)}₂(µ-H)(H)

(2d ), which were formed as a result of two Si-C(aryl)

bond scissions, were also observed in the mixture

between 3b-syn and 3b-a n ti was estimated at 55:45 by

¹H NMR spectroscopy. Although the syn/anti ratio did

not seemingly change in the temperature range from

-50 to 70 °C, it was considered that the ratio was

determined thermodynamically rather than kinetically.

Reaction of the syn and anti mixture of 3b with

trimethylphosphine resulted in exclusive formation of

the syn isomer, and elimination of the coordinated PMe₃

resulted in re-formation of the syn and anti mixture of

3b (vide infra). This result implied equilibrium between

3b-syn and 3b-a n ti. In addition, rotation of the bridging

silylene ligand within the NMR time scale was clearly

shown in the VT-NMR studies of the mixed-bridge bis-

(µ-silylene) complex {Cp*Ru(µ-H)}₂(µ-SiMe₂)(µ-SiPhMe)

(3c; vide infra).

(18) (a) Ciriano, M.; Gree, M.; Howard, J . A. K.; Proud, J .; Spencer,

J . L.; Stone, F. G. A.; Tsipis, C. A. J . Chem. Soc., Dalton Trans. 1978,

801-808. (b) Auburn, M.; Ciriano, M.; Howard, J . A. K.; Murray, M.;

Pugh, N, J .; Spencer, J . L.; Stone, F. G. A.; Woodward, P. J . Chem.

Soc., Dalton Trans. 1980, 659-666.

(19) (a) J ones, W. D.; Feher, F. J . J . Am. Chem. Soc. 1986, 108,

4814-4819. (b) J ones, W. D.; Feher, F. J . J . Am. Chem. Soc. 1985,

107, 620-631. (c) J ones, W. D.; Feher, F. J . Inorg. Chem. 1984, 23,

2376-2388. (d) J ones, W. D.; Feher, F. J . J . Am. Chem. Soc. 1984,

106, 1650-1663. (e) J ones, W. D.; Feher, F. J . Organometallics 1983,

2, 686-687. (f) J ones, W. D.; Feher, F. J . J . Am. Chem. Soc. 1982,

104, 4240-4242. (g) Belt, S. T.; Duckett, S. B.; Helliwell, M.; Perutz,

R. N. J . Chem. Soc., Chem. Commun. 1989, 928-930. (h) Belt, S. T.;

Dong, L.; Duckett, S. B.; J ones, W. D.; Partridge, M. G.; Perutz, R. N.

J . Chem. Soc., Chem. Commun. 1991, 266-269. (i) Chin, R. M.; Dong,

L.; Duckett, S. B.; Partridge, M. G.; J ones, W. D.; Perutz, R. N. J . Am.

Chem. Soc. 1993, 115, 7685-7695.

Unlike the reaction of 1 with Ph₃SiH, the mono(µ-

silylene) complex was not obtained at all, even in the

reaction with less than 2 molar equiv of Ph₂MeSiH. This

is probably due to the smaller steric bulk of Ph₂MeSiH

than that of Ph₃SiH.

In this reaction, Si-C(aryl) bond cleavage of Ph₂-

MeSiH predominated over Si-C(sp³) bond cleavage. Si-

C(sp³) bond cleavage to form a µ-SiPh₂bridge did not

take place. Preference of Si-C(aryl) bond cleavage over

that of the Si-C(sp³) bond has been also observed in

the thermolysis of the diplatinum silyl complex {Pt-

(PR₃)(SiPhMe₂)(µ-H)}₂(R ) C₆H₁₁), which resulted in

3860 Organometallics, Vol. 22, No. 19, 2003

Takao et al.

(determined by the FD-MS spectra of the crude mix-

ture).

The bis(µ-silyl) complex 2c was formed by the reaction

of 3c with liberated dihydrogen during the reaction of

1 with PhMe₂SiH. The reaction of bis(µ-silylene) com-

plex 3 with dihydrogen to yield the bis(µ-silyl) complex

2 is described later. Therefore, it was required to remove

dihydrogen to raise the selectivity of 3c. The yield of

3c increased up to 80% by bubbling argon to remove

1

H₂from the solution (determined by the H NMR) (eq

3). The yield of 3d was estimated at 5% on the basis of

Figu r e 3. Molecular structure of {Cp*Ru(µ-H)}₂(µ-SiPhMe)-

(µ-SiMe₂) (3c), with thermal ellipsoids at the 30% prob-

ability level.

Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles

(d eg) for 3c

Ru(1)-Ru(2)

Ru(1)-Si(1)

Ru(1)-Si(2)

Ru(1)-H(1)

Ru(1)-H(2)

Ru(2)-Si(1)

Ru(2)-Si(2)

Ru(2)-H(1)

Ru(2)-H(2)

Si(1)-C(1)

Si(1)-C(2)

Si(2)-C(3)

Si(2)-C(4)

2.6617(10)

2.355(2)

2.353(2)

1.7744(7)

1.8811(6)

2.360(2)

2.345(2)

1.7717(6)

1.8437(7)

1.899(8)

1.888(9)

1.884(7)

1.895(8)

Ru(3)-Ru(4)

Ru(3)-Si(3)

Ru(3)-Si(4)

Ru(3)-H(3)

Ru(3)-H(4)

Ru(4)-Si(3)

Ru(4)-Si(4)

Ru(4)-H(3)

Ru(4)-H(4)

Si(3)-C(30)

Si(3)-C(31)

Si(4)-C(32)

Si(4)-C(33)

2.6652(10)

2.364(2)

2.3528(19)

1.9146(6)

1.7367(7)

2.363(2)

2.3568(19)

1.7778(7)

1.8297(6)

1.893(7)

the ¹H NMR spectra. Analytically pure 3c was obtained

by recrystallization from cold pentane solution. Complex

1.883(7)

1.878(7)

1.876(7)

1

3c was fully characterized on the basis of H, ¹³C, and

²⁹Si NMR, IR, and FD-MS spectra.

1

In the H NMR spectra of 3c, a singlet assignable to

Ru(2)-Ru(1)-Si(1)

Ru(2)-Ru(1)-Si(2)

Si(1)-Ru(1)-Si(2)

Ru(1)-Ru(2)-Si(1)

Ru(1)-Ru(2)-Si(2)

Si(1)-Ru(2)-Si(2)

Ru(1)-Si(1)-Ru(2)

C(1)-Si(1)-C(2)

55.72(5) Ru(4)-Ru(3)-Si(3)

55.34(5) Ru(4)-Ru(3)-Si(4)

110.99(7) Si(3)-Ru(3)-Si(4)

55.54(5) Ru(3)-Ru(4)-Si(3)

55.62(5) Ru(3)-Ru(4)-Si(4)

111.08(7) Si(3)-Ru(4)-Si(4)

68.74(6) Ru(3)-Si(3)-Ru(4)

105.6(5)

69.03(6) Ru(3)-Si(4)-Ru(4)

107.4(4) C(32)-Si(4)-C(33) 106.1(4)

55.67(5)

55.60(5)

111.20(7)

55.70(5)

55.46(5)

111.10(7)

68.63(5)

the Cp* groups was observed at δ 1.65. At -60 °C, three

singlet signals assignable to the methyl groups on the

bridging silicon atoms were observed at δ 0.97, 0.79, and

0.74, respectively. Resonance for the phenyl group of 3c

was found at between δ 7.7 and 6.7. Observation of these

three methyl signals and one phenyl group shows the

mixed-bridge structure of 3c. Two doublets of the

C(30)-Si(3)-C(31) 103.5(4)

Ru(1)-Si(2)-Ru(2)

C(3)-Si(2)-C(4)

68.93(5)

hydride ligands were observed at δ -20.44 (d, J _H-H

)

6.0 Hz) and -21.13 (d, J _H-H) 6.0 Hz), which coalesced

into one signal at -5 °C. This indicated that an

intramolecular site-exchange process of the hydride

ligands occurred in 3c. Activation parameters for the

fluxional process were estimated at ∆H^q) 16.4 ( 0.7

kcal mol^-1and ∆S^q) 15.5 ( 2.6 cal mol^-1K^-1. These

were very similar to those of 3b-syn (∆H^q) 16.7 ( 0.4

kcal mol^-1and ∆S^q) 12.5 ( 1.6 cal mol^-1K^-1).

Since the yield of 3d was very low and isolation of 3d

was difficult, spectral data of 3d were not fully obtained.

It was characterized on the basis of the ¹H NMR spectra

and FD-MS analysis of the mixture. A nonfluxional

singlet signal of the hydride observed at δ -21.16, which

is typical for the bis(µ-silylene) complexes 3, implied the

highly symmetrical structure of 3d . The FD-MS analysis

of the crude products was quite consistent with the

existence of two µ-SiMe₂bridges in 3d .

assignable to the methyl group of the µ-SiPhMe bridge

did not change at any temperature, the signals observed

at δ 0.79 and 0.74 coalesced into one signal at 90 °C.

Activation parameters for the dynamic process were

estimated at ∆H^q) 16.5 ( 0.7 kcal mol^-1and ∆S^q

)

-7.8 ( 2.1 cal mol^-1K^-1by means of the line-shape

analysis. These parameters are considerably different

from those of the hydride site-exchange process, which

implies that these fluxional processes occur indepen-

dently.

X-ray diffraction studies were carried out using a red

single crystal of 3c. An ORTEP diagram of 3c is depicted

in Figure 3, and selected bond distances and angles are

listed in Table 3. The structure clearly shows the

µ-SiPhMe bridge formed via Si-C(sp³) bond cleavage.

Since there were two independent molecules in the unit

cell, one of them was represented.

The Ru-Ru distance of 2.663 Å (av) is similar to that

of 3a and implies existence of an RudRu double bond.

Ru-Si lengths are also the same as those of 3a and lie

In addition to the site-exchange process of the hydride

ligands, coalescence of the methyl protons of the µ-SiMe₂

group was observed at higher temperature. While the

shape of the methyl signal observed at δ 0.97 that was

Bond Cleavage of Tertiary Silanes on Ru₂Centers

Organometallics, Vol. 22, No. 19, 2003 3861

in the range of Ru-Si single-bond lengths. The acute

Ru-Si-Ru angles indicate strong interaction between

two ruthenium atoms, which was also observed in 3a .¹⁵

Cleavage of an Si-C(aryl) bond proceeds more readily

than that of an Si-C(sp³) bond due to prior π-coordina-

tion through the aryl group. Indeed, in the reaction of

1 with Ph₂MeSiH, Si-C(aryl) bond scission took place

with 100% selectivity. While the dimethylsilylene bridge

of 3c was formed via Si-C(aryl) bond cleavage, the

phenylmethylsilylene bridge was apparently formed via

Si-C(sp³) bond cleavage, which was seemingly unfavor-

able. A similarly curious preference was also seen in

the reaction of a µ-di-tert-butyl silane complex with

diethylsilane to yield the bis(µ-silyl) complex (Cp*Ru)₂-

(µ-η²-HSi^tBu₂)(µ-η²-HSiEtH)(µ-H)(H) (2e);^7bSi-C(sp³)

bond cleavage took precedence over that of the Si-H

bond. The reason for the exclusive Si-C(sp³) bond

cleavage is still unclear, but these Si-C bond cleavages

were only achieved by the cooperative effect of the

adjacent ruthenium centers.

F igu r e 4. Molecular structure of {Cp*Ru(µ-H)}₂(µ-SiM-

eEt) (4b), with thermal ellipsoids at the 30% probability

level.

Complex 1 did not react with phenyltrimethylsilane,

which has no Si-H bond. This indicates that initial

interaction of an Si-H bond to a ruthenium center was

essential for these Si-C bond cleavages. This result

implied the path of multimetallic activation and the

importance of the adjacent metal centers for activating

the Si-C bonds.

Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles

(d eg) for 4b

Ru(1)-Ru(2)

Ru(1)-Si(1)

Ru(2)-Si(1)

2.4492(9)

2.356(2)

2.361(2)

Si(1)-C(1)

Si(1)-C(2)

1.96(2)

1.89(1)

Ru(2)-Ru(1)-Si(1) 58.80(6) Ru(1)-Ru(2)-Si(1)

Ru(1)-Si(1)-Ru(2) 62.56(6) C(1)-Si(1)-C(2)

58.64(5)

101.9(9)

Rea ction of Cp *Ru (µ-H)₄Ru Cp * w ith R(CH₂d

CH)SiH₂(R ) Me, P h ). In the reaction of 1 with

secondary silane, such as Ph₂SiH₂and Et₂SiH₂, 2 molar

equiv of silane was consumed to form the bis(µ-silyl)

complex {Cp*Ru(µ-η²-HSiR₂)}₂(µ-H)(H) (2a , R dPh; 2e,

R ) Et).^7aIn contrast, the reaction with the second

silane molecule was suppressed due to the intramolecu-

lar coordination of the substituents on the silane in the

case that the silane contained substituents having

coordination ability to a metal center. Treatment of 1

with the dihydrovinylsilane R(CH₂dCH)SiH₂resulted

in the exclusive formation of the mono(µ-silylene)

complex {Cp*Ru(µ-H)}₂(µ-SiREt) (4b, R ) Me; 4c, R )

Ph; eq 4). Complexes 4b,c were isolated in analytically

downfield shift of a ²⁹Si signal is typical of a bridging

silylene ligand in a dinuclear complex containing an

M-M interaction.⁵The ²⁹Si signals of 4c (Ph, Et) and

4a (Ph, Ph) were also observed at lower magnetic field:

at δ 291.7 and 265.0, respectively. With an increase in

the number of phenyl groups on the bridging silicon,

the ²⁹Si resonance of the mono(µ-silylene) complex

shifted toward higher magnetic field. Such a trend was

also found in bis(µ-silylene) complexes 3.

Complex 1 reacts with only one molecule of vinyl-

silane, which contains an additional functional group

besides an Si-H bond. Since the vinyl group and the

Si-H bond occupied the vacant sites on the ruthenium

centers effectively, coordination of the second molecule

of vinylsilane would be suppressed. In the case of

formation of the mono(µ-silylene) complex 4a , which was

obtained by the reaction of 1 with Ph₃SiH, coordination

of the second silane was most likely suppressed by the

steric hindrance of Ph₃SiH. The coordinated vinyl group,

then, underwent hydrogenation by way of insertion into

an Ru-H bond followed by reductive elimination.

Whereas the site-exchange process of the hydride

ligands of bis(µ-silylene) complexes 3 was observed, it

was revealed that mono(µ-silylene) complexes 4 were

nonfluxional, at least on the NMR time scale, in the

temperature range of 20-100 °C. Shapes of the hydride

ligands were still sharp doublets, even at 100 °C.

Different reactivities of mono(µ-silylene) complexes 4 in

comparison to that of bis(µ-silylene) complexes 3 seemed

to stem from such nonfluxionality.

pure form by rinsing with pentane and fully character-

ized on the basis of ¹H, ¹³C, and ²⁹Si NMR and IR

spectral data as well as analytical data.

In the ¹H NMR spectrum of 4b, a singlet signal

assignable to methyl protons of the Cp* groups was

observed at δ 1.77. Two doublets of hydride ligands were

observed at δ -14.60 (d, J _H-H) 3.7 Hz) and -14.69 (d,

J _H-H) 3.7 Hz), respectively. A couple of a quartet and

a triplet assignable to an ethyl group on the bridging

silicon atom was observed at δ 1.43 (q, J _H-H) 7.7 Hz)

and 1.71 (t, J _H-H) 7.7 Hz), respectively.

An X-ray diffraction study was carried out using a

red single crystal of 4b. An ORTEP diagram of 4b is

depicted in Figure 4, and selected bond distances and

angles are listed in Table 4. Bond lengths and angles

are similar to those of the µ-diphenylsilylene complex

4a . Two Cp* groups were located nearly parallel to each

other; the angle between the centroids of the Cp* groups

The ²⁹Si signal of 4b (Me, Et) was observed at an

extremely low-field region (δ 310.8). Such a large

3862 Organometallics, Vol. 22, No. 19, 2003

Takao et al.

the back side to the front side of the Ru₂Si₂plane.

Oxidative addition of the Si-H bond of the intermediate

A then affords the cis type intermediate B. Recently,

we reported a similar site-exchange reaction via the

formation of an intermediary µ-silyl complex during the

site exchange of the hydride ligand of the µ-silylene

µ-ethylidyne complex (Cp*Ru)₂(µ-SiMe₂)(µ-CCH₃)-

(µ-H),^11band the existence of such a cis-type intermedi-

ate was implied by the reaction of a mixture of 3b-syn /

a n ti with PMe₃(vide infra).

There are two possible pathways to account for the

site-exchange process from the cis type intermediate B.

In path A, reductive elimination between the other

µ-silylene bridge and H^bto form the intermediate A′

would take place. The hydride H^bthen migrates to the

back side of the Ru₂Si₂plane by rotation of the µ-silyl

group of A′, and as a result, H^aand H^bmutually

exchange the coordination site without change in the

orientation of the substituents on the bridging silicon

atoms. Path B includes reductive coupling between H^a

and H^bto form the η²-hydrogen intermediate C. Rota-

tion of the η²-H₂ligand on the ruthenium center would

result in site exchange between H^aand H^b.

Complex 3c has both µ-SiPhMe and µ-SiMe₂bridges.

It is likely that the energy barrier to make an Si-H

bond is different. Lichtenberger et al. have shown that

electron-withdrawing substituents on the silicon pro-

mote the oxidative addition of an Si-H bond due to

lowering the energy level of σ*(Si-H).²⁰Therefore, it

seems to be preferable to form a µ-HSiMe₂group rather

than to form a µ-HSiPhMe group during the site-

exchange reaction.

F igu r e 5. Variable-temperature ¹H NMR spectra of

{Cp*Ru(µ-H)}₂(µ-SiMe₂)(µ-SiPhMe) (3c) in THF-d₈showing

hydride signals (left) and results of the simulation (right).

The small signal appearing at δ -21.16 was assignable to

the hydride signal of the bis(µ-silylene) complex {Cp*Ru-

(µ-SiMe₂)(µ-H)}₂(3d ).

There were, however, no distinct differences between

the activation parameters of 3c and 3b-syn . There were

two possible explanations for this result. The first

explanation is that formation of the µ-HSiPhMe group

was involved in the rate-determining step in both

processes of 3c and 3b-syn . Since formation and rotation

of the two silyl ligands were required for the hydride

site exchange by path A in Scheme 3, the step of the

formation of µ-HSiPhMe, which was considered to be

higher than that of µ-HSiMe₂, would be included in both

cases. The second explanation is that the step of

formation and cleavage of an intermediary Si-H bond

is not involved in the rate-determining step of the

fluxional process. The kinetic parameters for 3c and 3b

are almost the same, regardless of the substituents on

the silicon atoms. Therefore, the site-exchange process

of the hydrides most likely proceeds via the intermedi-

ary η²-hydrogen complex C (path B in Scheme 3).

It is difficult to conclude whether path A or path B is

plausible at this stage, because both complexes, 3c and

3b, have the µ-SiPhMe bridge. We are now trying to

synthesize another type of mixed-bridge bis(µ-silylene)

complex not containing a µ-SiPhMe bridge, and infor-

mation about the mechanism would be obtained in

detail by VT-NMR studies on these complexes.

and the Ru-Ru vector was ca. 3°. The Ru-Ru distance

of 2.4492(9) Å corresponds to an RutRu triple bond. The

Ru-Si lengths (average 2.359 Å) lie in the range of the

reported value for a Ru-Si σ-bond and are similar to

those of 4a and bis(µ-silylene) complexes 3a ,c.

F lu xion a l Beh a vior of Bis(µ-silylen e) Com p lex

3. (1) Site Exch a n ge of th e Hyd r id e Liga n d s. As

mentioned above, the site-exchange process of the

hydride ligands took place in bis(µ-silylene) complexes

3. Hydride signals of 3c measured at various temper-

atures are depicted in Figure 5 together with simulated

signals. At -60 °C, the exchange process reached the

slow-exchange limit and two sharp doublets of hydride

ligands were found at δ -20.44 and -21.13. They began

to exchange with an increase in temperature. The

activation parameters of this process of 3c were calcu-

lated on the basis of the Eyring plot using the exchange

rate constant k obtained from the line-shape analysis;

∆H^q) 16.4 ( 0.7 kcal mol^-1, ∆S^q) 15.5 ( 2.6 cal mol^-1

K^-1. Those for 3b-syn were also estimated at ∆H^q) 16.7

( 0.4 kcal mol^-1and ∆S^q) 12.5 ( 1.6 cal mol^-1K^-1

.

The X-ray diffraction study of 3c showed that the

silicon atoms were σ-bonded to two ruthenium atoms,

The ²⁹Si signals of bis(µ-silylene) complexes 3 were

observed around δ 110 (3a , δ 109.8; 3b-syn /a n ti, δ

108.2, 107.7; 3c, δ 112.3, 107.9), which were consider-

2

and the small J _Si-Hvalue, 7-8 Hz, also showed that

direct bonding interaction between Si and H was

negligible. However, the existence of an intermediary

species A having an Si-H bonding interaction is pro-

posed in the site-exchange process (Scheme 3). Through

rotation of the silyl group around the Ru-Si bond in

the intermediate A, the hydride ligand migrates from

(20) (a) Lightenberger, D. L.; Rai-Chaudhuri, A. J . Am. Chem. Soc.

1989, 111, 3583-3591. (b) Lightenberger, D. L.; Rai-Chaudhuri, A.

Inorg. Chem. 1990, 29, 975-981. (c) Lightenberger, D. L.; Rai-

Chaudhuri, A. Organometallics 1990, 9, 1686-1690. (d) Lightenberger,

D. L.; Rai-Chaudhuri, A. J . Am. Chem. Soc. 1990, 112, 2492-2497.

Bond Cleavage of Tertiary Silanes on Ru₂Centers

Organometallics, Vol. 22, No. 19, 2003 3863

Sch em e 3^a

a

Ru ) (C₅Me₅)Ru.

Ch a r t 1

ably higher than the reported values for the bridging

silylene atoms. They were much different from those of

mono(µ-silylene) complexes (4a , δ 265.0; 4b, δ 310.8; 4c,

δ 291.7), despite the fact that they have similar struc-

tures around the bridging silicon atom. The reason the

²⁹Si signals of 3 appeared at higher region is most likely

due to the fluxional process in which the intermediary

Si-H bonds were held. They were rather close to those

for bis(µ-silyl) complexes having 2e-3c Ru-H-Si in-

teractions. The ²⁹Si signals of {Cp*Ru(µ-η²-HSiPh₂)}₂-

(µ-H)(H) (2a ) and {Cp*Ru(µ-η²-HSiPhMe)}₂(µ-H)(H) (2b-

syn ) were observed at δ 95.1 and 101.9, respectively.

Although J _Si-Hvalues of these bis(µ-silylene) complexes

3 were determined to be less than 10 Hz from the

RudSi bond is often proposed for some isomerization

of µ-silylene complexes,^8j,21it would bring about a larger

positive ∆S^qvalue due to steric repulsion between two

Cp* groups. The ∆S^qvalue of -8 cal mol^-1K^-1is very

similar to the site-exchange process of the methyl groups

of (Cp*Ru)₂(µ-SiMe₂)(µ-CCH₃)(µ-H) (∆H^q) 12.5 ( 0.1

1

observed satellite signals in the H NMR spectra, the

bridging silicon ligand of 3 seems to have some contri-

bution of a µ-silyl ligand in solution. Downfield shifts

of the ²⁹Si signals of mono(µ-silylene) complexes 4 were

thus most likely attributed to a lack of Si-H interaction.

This is the significantly different point between com-

plexes 3 and 4 in their properties.

kcal mol^-1, ∆S^q) -7.7 ( 0.4 cal mol^-1K^{-1 11b}

by way

)

of a 1,2-shift of the intermediary silyl group (path B in

Scheme 4). Migration of the silyl group between the two

ruthenium nuclei proceeded with retention of the ster-

eochemistry at the silicon atom. Oxidative addition of

the Si-H bond at Ru²resulted in the isomerization

between syn and anti forms (inversion of the µ-silylene

ligand). Migration of the PR₃group on the diruthenium

skeleton with retention at the phosphorus atom was

reported in our preceding paper, and the transition state

of the dynamic process was proposed by the aid of DFT

calculations.²²Girolami et al. have also reported the 1,2-

shift of a silyl group on the diruthenium complex

(Cp*Ru)₂(µ-CH₂)(SiMe₃)(Cl). In this process, the activa-

(2) Rota tion of th e Br id gin g Silicon Atom . The

site-exchange reaction of the methyl groups on the

µ-SiMe₂bridge also took place in 3c (Chart 1) at higher

temperature (Figure 6). Line-shape analysis of this

fluxional process revealed that the site-exchange process

of the methyl groups took place independently of that

of the hydride ligands (∆H^q) 16.5 ( 0.7 kcal mol^-1

,

∆S^q) -7.8 ( 2.1 cal mol^-1K^-1).

There were two possible pathways of the site ex-

change of the methyl groups between the syn methyl

group and that anti to the phenyl group. Path A involves

isomerization of the µ-SiMe₂(or µ-SiPhMe) ligand to a

terminally bonded silylene ligand followed by rotation

around an RudSi bond. Path B involves a 1,2-shift of

the intermediary µ-silyl ligand. Although rotation of the

(21) Kummer, D.; Furrer, J . Z. Naturforsch., B 1971, 26B, 162-

163.

(22) Ohki, Y.; Suzuki, H. Angew. Chem., Int. Ed. 2002, 41, 2994-

2997.

3864 Organometallics, Vol. 22, No. 19, 2003

Takao et al.

PMe₃coordinated in 5 was readily liberated upon

heating, and a thermodynamic mixture of two diaster-

eomers of 3b (syn:anti ) 55:45) was recovered. This

showed an occurrence of geometrical change from syn

to anti with respect to the silylene bridges, and this

geometrical change is probably a result of rotation of

the silylene group around the Ru-Si bond. The bis(µ-

silylene) complex 5 was fully characterized on the basis

of ¹H, ¹³C, ²⁹Si, and ³¹P NMR and IR spectra as well as

elemental analysis.

In the ¹H NMR spectra measured at 23 °C, two

singlets with the same intensity assignable to the Cp*

groups were observed at δ 1.20 and 1.84. The former

was observed as a doublet with a coupling constant of

J _P-H) 0.7 Hz. This strongly indicates that the PMe₃

ligand is coordinated to one of the two ruthenium

centers as a terminal ligand. In contrast, the hydride

signal was observed as a singlet at δ -13.06 with an

intensity ratio of 2H. This indicates terminal coordina-

tion of these hydride ligands to the ruthenium atom

which has no bonding interaction with the phosphine

ligand. A sharp absorption attributable to ν(Ru-H) was

observed at 2036 cm^-1in the IR spectrum of 5.

The two methyl groups on the bridging silicon atoms

were observed to be equivalent. This indicates that 5

adopts a syn form with respect to the orientation of the

two µ-SiPhMe groups. The ²⁹Si signal of 5 was observed

at δ 205.2 as a doublet peak with a coupling constant

of J _Si-P) 20.5 Hz.

F igu r e 6. Variable-temperature ¹H NMR spectra of

{Cp*Ru(µ-H)}₂(µ-SiMe₂)(µ-SiPhMe) (3c) in toluene-d₈show-

ing methyl signals (left) and results of simulation (right).

The small signal marked with an asterisk appearing at δ

0.97 at 10 °C was assignable to the methyl signal of the

bis(µ-silylene) complex {Cp*Ru(µ-SiMe₂)(µ-H)}₂(3d ).

tion parameters, ∆H^qand ∆S^q, were estimated at 9.0 (

0.2 kcal mol^-1and 0.5 ( 0.8 cal mol^-1K^-1, respec-

tively.²³

Although isomerization between 3b-syn and 3b-a n ti

was not observed in the VT-NMR study, which was most

likely due to the small difference in ∆S°, isomerization

of 3b-a n ti to the syn form was confirmed in the reaction

of a mixture of 3b-syn /a n ti with PMe₃. This isomer-

ization is also considered to proceed via the 1,2-shift of

an intermediary µ-silyl group.

Rea ction of a Mixtu r e of th e Bis(µ-p h en ylm eth -

ylsilylen e) Com p lex 3b w ith P Me₃: A Tr a p p ed

Com p lex of th e cis-Bis(µ-silylen e) In ter m ed ia te by

P Me₃. While bis(µ-diphenylsilylene) complex 3a did not

react with PMe₃irrespective of reaction temperature,

treatment of a mixture of the two diastereomers 3b-

syn /a n ti with a small excess amount of PMe₃afforded

bis(µ-silylene) complex {Cp*Ru(µ-SiPhMe)}₂(PMe₃)(H)₂

(5) as the sole product (eq 5). Notably, only syn-5 was

obtained during the reaction, although the reaction was

carried out using a mixture of syn and anti isomers. The

At -40 °C, two signals assignable to the methyl

protons of PMe₃were observed at δ 1.35 (d, 6H, J _P-H

)

7.9 Hz) and 1.11 (d, 3H, J _P-H) 7.9 Hz), respectively.

These signals coalesced into one signal at 60 °C. Free

rotation around the Ru-P bond was interrupted, most

likely due to steric repulsion between two Si-Me groups

and one P-Me group. An X-ray diffraction study

revealed that one P-C bond lay between two Si-Me

groups, which was clearly shown in a space-filling model

of the Ru₂Si₂P moiety (Figure 8).

X-ray diffraction studies were carried out using a

yellow single crystal of 5 obtained from cold pentane

solution. An ORTEP diagram of 5 is depicted in Figure

7, and selected bond distances and angles are listed in

(23) (a) Lin, W.; Wilson, S. R.; Girolami, G. S. J . Am. Chem. Soc.

1993, 115, 3022-3023. (b) Lin, W.; Wilson, S. R.; Girolami, G. S.

Organometallics 1991, 13, 2309-2319.

Bond Cleavage of Tertiary Silanes on Ru₂Centers

Organometallics, Vol. 22, No. 19, 2003 3865

Sch em e 4^a

a

Ru ) (C₅Me₅)Ru.

Despite the steric repulsion between the P-Me and

the Si-Me groups implied on the basis of the VT-NMR

study of 5, apparent elongation of the Ru(1)-P(1) bond

was not observed. The steric repulsion was clearly

reflected in the bond angles. The value of 95.5° for the

C-Si-C angle was considerably small for an sp³silicon

atom, and the Ru(1)-P(1)-C(1) angle is larger than

Ru(1)-P(1)-C(2) and Ru(1)-P(1)-C(3) by ca. 10°. The

Ru(1)-P(1) length lies in the normal range of the

reported Ru-P bond lengths in the [Cp*Ru(PMe₃)] unit

(2.258-2.374 Å).²⁴The Ru(1)-P(1) length of 2.260(2) Å

is almost the same as that observed in {Cp*Ru(µ-H)}₂-

(PMe₃) (2.278(5) Å), which was obtained by the reaction

of 1 with PMe₃.²²All of the Ru-Si lengths also lie in

the normal range for Ru-Si σ-bonds.

Either 3b-syn or 3b-a n ti reacts with PMe₃to afford

the syn isomer of 5, whose methyl groups on the

bridging silicon atom occupy the axial positions. Thus,

during this reaction, the syn/anti isomerization took

place simultaneously with the cis/trans isomerization

of the bis(µ-silylene) complex. As mentioned above, the

syn to anti ratio of 3b did not change at least up to 70

°C. This means that isomerization from 3b -a n ti to

3b-syn was slow or did not proceed at ambient temper-

F igu r e 7. Molecular structure of {Cp*Ru(µ-SiPhMe)}₂-

(PMe₃)(H)₂(5), with thermal ellipsoids at the 30% prob-

ability level.

Table 5. Location of the terminal hydride ligands was

determined during Fourier synthesis and refined iso-

tropically. The Ru(1)-Ru(2) distance (3.0159(18) Å)

indicated there was a single bonding interaction be-

tween two ruthenium atoms. Each metal center satisfied

the EAN rule from consideration of a single Ru-Ru

bond.

It was clearly seen in Figure 7 that two hydride

ligands and two silylene ligands were both attached to

Ru(2) in a cis fashion. Bridging SiPhMe groups in 5 are

mutually cis with respect to the Ru-Ru vector, and 5

is likely formed as a result of capture of the intermedi-

ary cis-silylene species proposed in the site exchange of

the hydride ligands.

(24) For example: (a) Straus, D. A.; Tilley, T. D.; Reingold, A. L.;

Geib, S. J . J . Am. Chem. Soc. 1987, 109, 5872-5873. (b) Lehmkuhl,

H.; Schwickardi, R.; Kruger, C.; Raabe, G. Z. Anorg. Allg. Chem. 1990,

581, 41-47. (c) Grumbine, S. D.; Chadha, R. K.; Tilley, T. D. J . Am.

Chem. Soc. 1992, 114, 1518-1520. (d) Schenk, W. A.; Urban, P.;

Dombrowski, E. Chem. Ber. 1993, 126, 679-684. (e) Grunbine, S. K.;

Tilley, T. D.; Arnold, F. P.; Rheingold, A. L. J . Am. Chem. Soc. 1994,

116, 5495-5496. (f) Dombrowski, E.; Schenk, W. A. Angew. Chem.,

Int. Ed. Engl. 1995, 34, 1008-1009. (g) Mitchell, G. P.; Tilley, T. D. J .

Am. Chem. Soc. 1997, 119, 11236-11243. (h) Grumbine, S. K.; Mitchell,

G. P.; Straus, D. A.; Tilley, T. D.; Rheingold, A. L. Organometallics

1998, 17, 5607-5619. (i) Smith, D. C., J r.; Haar, C. M.; Luo, L.; Li, C.;

Cucullu, M. E.; Mahler, C. H.; Nolan, S. P.; Marshall, W. J .; J ones, N.

L.; Fagan, P. J . Organometallics 1999, 18, 2357-2361. (j) Kawano,

Y.; Shimoi, M. Chem. Lett. 1999, 489-490.

3866 Organometallics, Vol. 22, No. 19, 2003

Takao et al.

F igu r e 8. Space-filling model of the Ru₂Si₂P moiety of complex 5: (A) top view; (B) side view.

Ta ble 5. Selected Bon d Dista n ces (Å) a n d An gles

(d eg) for 5

complex 3a with 1 atm of H₂took 48 h at 25 °C,

formation of 2c was accomplished within 2 h under 1

atm of H₂atmosphere.

Ru(1)-Ru(2)

Ru(1)-Si(1)

Ru(2)-Si(1)

Ru(2)-H(1)

P(1)-C(1)

3.0159(18)

2.358(2)

2.391(3)

1.66(7)

1.832(10)

1.824(10)

1.924(8)

1.912(9)

Ru(1)-P(1)

Ru(1)-Si(2)

Ru(2)-Si(2)

Ru(2)-H(2)

P(1)-C(2)

Si(1)-C(4)

Si(2)-C(11)

2.260(2)

2.365(3)

2.382(3)

1.75(8)

1.841(9)

1.926(9)

1.917(9)

P(1)-C(3)

Si(1)-C(5)

Si(2)-C(12)

Si(1)-Ru(1)-Si(2)

H(1)-Ru(2)-H(2)

Ru(1)-P(1)-C(2)

Ru(1)-Si(1)-Ru(2)

C(4)-Si(1)-C(5)

98.27(8) Si(1)-Ru(2)-Si(2)

96.90(8)

124.3(4)

115.9(4)

78.90(7)

96.8(4)

62(4)

Ru(1)-P(1)-C(1)

Ru(1)-P(1)-C(3)

113.9(4)

78.85(7) Ru(1)-Si(2)-Ru(2)

94.1(4)

C(11)-Si(2)-C(12)

ature. Therefore, trimethylphosphine seemed to cause

the isomerization from the anti to the syn isomer.

In contrast to the syn/anti isomerization, the site

exchange of the hydride ligands of 3b took place at room

temperature at a considerable rate. This indicates that

the cis-bis(µ-silylene) intermediates would be generated

during the reaction independently of PMe₃(step A in

Scheme 5). Thus, the syn/anti isomerization involved

in step B in Scheme 5 should be accelerated by the

presence of PMe₃. Interaction of PMe₃with 3b would

afford a 34e intermediate, which was coordinatively

saturated. In this intermediate, rotation of the µ-silylene

bridge would be promoted due to the steric repulsion.

The reaction of 3b with PMe₃showed both cis/trans

and syn/anti isomerization occurring in the bis(µ-

silylene) complex, and this result is quite consistent with

the VT-NMR studies. Formation of the cis-bis(µ-silylene)

intermediate is the key step of the unique reactivity of

the bis(µ-silylene) complex 3. The reaction of 3a with

acetylene afforded a µ-disilaruthenacyclopentene com-

plex, which also adopted a cis form.^11aComplex 3 also

reacts with H₂and CO, as mentioned below. These

reactions were thought to proceed via formation of the

cis-bis(µ-silylene) intermediate.

Rea ction of Bis(µ-silylen e) Com p lex 3 w ith Di-

h yd r ogen : F or m a t ion of Bis(µ-silyl) Com p lex 2.

Treatment of bis(µ-silylene) complexes 3a -c with 1 atm

of dihydrogen at ambient temperature quantitatively

afforded thebis(µ-silyl)complexes {Cp*Ru(µ-η²-HSiR¹R²)}-

{Cp*Ru(µ-η²-HSiR³R⁴)}(µ-H)(H) (2a , R¹) R²) R³) R⁴

) Ph; 2b-syn and 2b-a n ti, R¹) R³) Ph, R²) R⁴)

Me; 2c, R¹) R²) R³) Me, R⁴) Ph), respectively (eq

6). The rate of hydrogenation of 3 significantly depended

on the substituents on the bridging silicon atoms. While

completion of the reaction of the bis(µ-diphenylsilylene)

The reverse reaction of eq 6, oxidative addition of the

η²-Si-H bonds of the bis(µ-silyl) complex 2, proceeds

more readily in 2a than in 2b-syn /a n ti. Complex 2c,

which has one phenyl group on the bridging silicon

atoms, did not undergo oxidative addition of the η²-Si-H

bonds upon heating in solution. On the other hand,

thermolysis of 2c resulted in decomposition to yield a

messy mixture. Complex 3c also gradually decomposed

even at -20 °C to yield a complex mixture, including

the diruthenium tetrahydride complex 1; the half-life

of 3c is about 1 month at -20 °C under an argon

atmosphere. Thus, thermal stability of the Ru-Si bond

in 3 is affected by the substituents on the bridging

silicon atoms as well as the rate of hydrogenation of 3.

It is known that an electron-withdrawing phenyl

group lowers the energy level of the σ*(Si-H). Thus, as

the number of phenyl groups is increased, oxidative

addition of the Si-H bond proceeds readily, and the

equilibrium is inclined toward the bis(µ-silylene) com-

plex. This is fully consistent with the photoelectron

Bond Cleavage of Tertiary Silanes on Ru₂Centers

Organometallics, Vol. 22, No. 19, 2003 3867

Sch em e 5

studies of silane complexes having 2e-3c M-H-Si

interactions performed by Lichtenberger et al.²⁰

electron complex. Thus, coordinative addition of the 2e

donor to 3 was anticipated. Since trimethylphosphine

was bulky, only one molecule was incorporated into 3b.

Furthermore, complex 3a did not react with PMe₃

because of steric repulsion between the four phenyl

groups and phosphine. In contrast to this, when using

carbon monoxide, which is a less bulky 2e donor, the

bis(µ-silylene) complex 3a reacts with 2 molar equiv of

CO. The reaction of 3a with carbon monoxide smoothly

proceeds at room temperature to form the dicarbonyl

complex {Cp*Ru(µ-SiPh₂)(CO)}₂(cis-6a ) (eq 7). The two

Complexes 2a ,e have been alternatively synthesized

by the reaction of 1 with Ph₂SiH₂and Et₂SiH₂,

respectively.^7aA diastereomeric mixture of the µ-phen-

ylmethylsilyl complex {Cp*Ru(µ-HSiPhMe)}₂(µ-H)(H)

(2b -syn /a n ti) was also obtained by the reaction of 1

with PhMeSiH₂.²⁵Whereas 3b-syn and 3b-a n ti could

not be separated by the use of column chromatography,

2b-syn and 2b-a n ti could be separated from each other.

Orientation of the substituents on the bridging silyl

groups of 2b-syn and 2b-a n ti could be determined by

1

the use of H NMR.

The mono(µ-silylene) complex 4 has both bridging

silylene and hydride ligands, and its structural param-

eters around the silicon atom were quite similar to those

of 3. Thus, formation of a mono(µ-silyl) or mono(µ-silane)

complex would be anticipated by the reaction with

dihydrogen. However, the reaction of 4 with dihydrogen

proceeded in a way considerably different from that of

3. While the bis(µ-silylene) complex 3 readily reacted

with dihydrogen at ambient temperature, the mono(µ-

silylene) complex 4 did not react with dihydrogen

without heating. Complex 4 only reacted under more

severe conditions; it required 100 °C and 7 atm of H₂.

Neither a mono(µ-silyl) nor a mono(µ-silane) complex

was obtained by the reaction. Instead, a mixture of

tetrahydride complex 1 and its thermolysis products was

obtained.²⁶Formation of 1 indicates liberation of the

bridging diphenylsilylene ligand, but the fate of the

bridging silylene moiety has not yet been clarified.

Rea ction of Bis(µ-silylen e) Com p lex 3 w ith Ca r -

bon Mon oxid e. The bis(µ-silylene) complex 3 was a 32-

CO groups were coordinated to the Ru₂Si₂plane in a

cis fashion. In a previous paper,^7awe proposed the

wrong geometry for the dicarbonyl complex formed in

the reaction of 3a with carbon monoxide. Here we

correct the structure of 6a for the mistakes in the

geometry of two carbonyl groups. The cis geometry of

6a was revealed by detailed spectroscopic studies as well

(25) Takao, T.; Suzuki, H. Unpublished results (see the Supporting

Information).

(26) Suzuki, H.; Omori, H.; Ito, Y. Unpublished results. Thermolysis

of a diruthenium tetrahydride complex in toluene at 100 °C afforded

a mixture of polyhydride clusters of {Cp*Ru(µ-H)}₃(µ₃-H)₂and (Cp*Ru)₄-

(H)₆in the ratio ca. 95:5.

3868 Organometallics, Vol. 22, No. 19, 2003

Takao et al.

as preliminary X-ray diffraction studies. Complex 6a

was fully characterized on the basis of ¹H, ¹³C, and ²⁹Si

NMR, IR, and FD-MS spectra as well as elemental

analysis.

tr a n s-6b-a n ti. Formation of 7 was confirmed on the

basis of the H NMR and IR spectra of the mixture.

1

A yellow single crystal of cis-6a was obtained from

cold toluene solution, but the quality was not good

enough for X-ray diffraction studies. However, cis

coordination of the two terminal CO ligands with respect

to the Ru₂Si₂plane was unquestionably confirmed (see

Figure S-1 in the Supporting Information).

The cis coordination of the CO ligands was also

confirmed by means of IR and ¹³C NMR spectroscopy.

In the IR spectrum of cis-6a , a band assignable to the

symmetric stretching mode of the carbonyl ligands was

observed at 1955 cm^-1, and that of the asymmetric mode

was observed at 1922 cm^-1as a shoulder peak. The

intensity ratio of ν_sym/ν_asymwas larger than 1, which

indicates cis coordination of the two CO ligands with

respect to the Ru₂Si₂plane. Observation of two sets of

¹³C signals of the phenyl groups in the ¹³C NMR spectra

also indicates cis coordination of the carbonyl ligands.

In the ²⁹Si NMR spectra of cis-6a , the resonance of

the bridging silylene ligand was observed at δ 211.4.

The remarkable downfield shift compared to that of 3a

(δ 109.8) can most likely be attributed to lack of

interaction between Si and H.

Only two isomers, cis-6b-syn and tr a n s-6b-a n ti,

were isolated by the use of column chromatography

followed by recrystallization. The major isomer was cis-

1

6b-syn , which was obtained in 70% yield. The H and

Ogino et al. reported thermal and photochemical

isomerization between cis- and trans-µ-silylene com-

plexes Cp₂Fe₂(CO)₂(µ-CO){µ-SiMe(SiMe₃)}, in which

cleavage of an Fe-Fe bond was involved.²⁷In the case

of 6a , however, formation of the trans isomer of 6a was

not observed during the reaction. The complex cis-6a

was thermally robust, and isomerization to the trans

isomer did not take place, at least at 150 °C. In contrast

to the mono(µ-silylene) mono(µ-carbonyl) diiron complex,

cleavage of the Ru-Ru bond followed by rotation around

the Ru-Si bond would not take place, since the two

ruthenium atoms of cis-6a were strongly bound by the

two bridging silicon atoms.

Although no intermediate was observed during the

reaction, the complex cis-6a would be formed via the

intermediary cis-bis(µ-silylene) complex in analogy to

the formation path of 5, and the hydride ligands were

substituted by the second CO molecule.

The diastereomeric mixture 3b-syn /a n ti also reacted

with carbon monoxide to give cis-6b -syn and tr a n s-

6b-a n ti (eq 8), but the reaction was much more com-

plicated; in the IR spectra of the obtained mixture,

several bands arising from the byproducts containing a

bridging carbonyl ligand were observed around 1750-

1800 cm^-1. The spectra indicate that the mono(µ-

silylene) complex {Cp*Ru(CO)}₂(µ-SiPhMe)(µ-CO) and

the diruthenium tetracarbonyl complex {Cp*Ru(CO)-

(µ-CO)}₂(7)²⁸were formed in addition to cis-6b-syn and

¹³C NMR spectra and IR spectrum of cis-6b-syn indi-

cated a cis geometry of the two carbonyl groups with

respect to the Ru₂Si₂plane, as in cis-6a , and the

orientation of the two bridging silicon atom was revealed

as a syn form similar to that of 5.

In the ¹H NMR spectra of cis-6b-syn , one singlet

assignable to the methyl group on the bridging silicon

was observed at δ 1.55. In the IR spectra of cis-6b-syn ,

ν_symand ν_asymwere observed at 1932 and 1903 cm^-1

,

respectively. The cis orientation of the two carbonyl

groups was confirmed by the fact that the intensity ratio

of ν_sym/ν_asymwas larger than 1.

In contrast to cis-6b-syn , tr a n s-6b-a n ti adopted a

trans form with respect to the Ru₂Si₂plane. In the IR

spectrum of tr a n s-6b-a n ti, only absorption assignable

to ν_asymwas observed at 1899 cm^-1. In addition to this,

only one signal assignable to the methyl groups on the

bridging silicon atoms was observed at δ 1.41. These

facts imply that two carbonyl groups coordinate to the

Ru₂Si₂plane in a trans fashion, and the orientation of

the two silicon atoms is an anti form.

Formation of the trans isomer was also observed in

the reaction of 3c with CO. The trans-dicarbonyl

complex {Cp*Ru(CO)}(µ-SiPhMe)(µ-SiMe₂) (tr a n s-6c)

was isolated in 37% yield among many products by the

1

use of column chromatography (eq 9). In the H NMR

spectrum of tr a n s-6c, two ¹H signals of the Cp* group

were observed at δ 1.61 and 1.74 with the same

intensity. This unquestionably indicates the trans ge-

ometry of 6c. Trans geometry was also confirmed by the

IR spectrum, showing a strong absorption assignable

(27) (a) Tobita, H.; Kawano, Y.; Shimoi, M.; Ogino, H. Chem. Lett.

1987, 2247-2250. (b) Tobita, H.; Kawano, Y.; Ogino, H. Chem. Lett.

1989, 2155-2158. (c) Ueno, K.; Hamashima, N.; Shimoi, M.; Ogino,

H. Organometallics 1991, 10, 959-962. (d) Kawano, Y.; Tobita, H.;

Ogino, H. J . Organomet. Chem. 1992, 428, 125-143. (e) Kawano, Y.;

Tobita, H.; Ogino, H. Organometallics 1992, 11, 499-500. (f) Kawano,

Y.; Tobita, H.; Shimoi, M.; Ogino, H. J . Am. Chem. Soc. 1994, 116,

8575-8581.

(28) (a) Davison, A.; McCleverty, J . A.; Wilkinson, G. J . Chem. Soc.

1963, 1133-1138. (b) King, R. B.; Iqbal, M. Z.; King, A. D., J r. J .

Organomet. Chem. 1979, 171, 53-63. (c) Steiner, A.; Gornitzka, H.;

Stalke, D.; Edelmann, F. T. J . Organomet. Chem. 1992, 431, C21-

C25.

to the asymmetric mode of ν(CO) at 1903 cm^-1

.

Rea ction of Mon o(µ-silylen e) Com p lexes 4 w ith

Ca r bon Mon oxid e. While the reaction of the mono(µ-

silylene) complex 4 with dihydrogen resulted in libera-

tion of the bridging silicon atom, a µ-carbonyl complex

containing a bridging silylene ligand was obtained in

the reaction of 4 with CO. The mono(µ-diphenylsilylene)

Bond Cleavage of Tertiary Silanes on Ru₂Centers

Organometallics, Vol. 22, No. 19, 2003 3869

F igu r e 9. Molecular structure of {Cp*Ru(CO)}₂(µ-SiPh₂)-

(µ-CO) (8a ), with thermal ellipsoids at the 30% probability

level.

complex 4a reacted with CO to afford a mixture of the

mono(µ-silylene) mono(µ-carbonyl) complex {Cp*Ru-

(CO)}(µ-SiPh₂)(µ-CO) (8) and the diruthenium tetracar-

bonyl complex {Cp*Ru(CO)(µ-CO)}₂(7)²⁸(eq 10). The

Ta ble 6. Selected Bon d Dista n ces (Å) a n d An gles

(d eg) for 8a

Ru(1)-Ru(2)

Ru(1)-C(1)

Ru(2)-Si(1)

Ru(2)-C(3)

Si(1)-C(10)

C(2)-O(2)

2.846(2)

2.04(2)

2.385(4)

1.84(2)

1.93(1)

1.20(2)

Ru(1)-Si(1)

Ru(1)-C(2)

Ru(2)-C(1)

Si(1)-C(4)

C(1)-O(1)

C(3)-O(3)

2.382(4)

1.77(2)

1.99(2)

1.92(1)

1.19(2)

1.14(2)

Si(1)-Ru(1)-C(1)

Ru(1)-Si(1)-Ru(2)

Ru(1)-C(1)-Ru(2)

Ru(2)-C(1)-O(1)

Ru(2)-C(3)-O(3)

97.6(5)

Si(1)-Ru(2)-C(1)

C(4)-Si(1)-C(10)

Ru(1)-C(1)-O(1)

Ru(1)-C(2)-O(2)

99.1(5)

96.8(6)

132(1)

174(1)

73.3(1)

89.9(6)

137(1)

178(1)

characterized,²⁸only 8a is shown in Figure 9. The two

terminal carbonyl ligands are arranged mutually trans

with respect to the Ru₂SiC plane.

The Ru-Ru distance of 2.846(2) Å corresponds to an

Ru-Ru single bond. The sum of the interior angles of

the Ru₂SiC core (359.9°) indicates that these four atoms

are located in the same plane. The Ru-Si distance

(average 2.38 Å) is slightly longer than those observed

in 3a (2.36 Å) and 4a (2.35 Å).

ratio between 7 and 8 prior to treatment for purification

was 3:10. Complex 8 was fully characterized by means

of ¹H, ¹³C, and ²⁹Si NMR, IR, and FD-MS spectroscopy.

In contrast to cis-6a , only the trans isomer was

obtained in this reaction. The trans form was confirmed

by the IR spectrum of 8. The IR spectrum of 8 exhibited

an absorption band at 1910 cm^-1. This is the only signal

observed in the region of 1800-2100 cm^-1and is

ascribed to ν_asym(CO). In addition, the stretching vibra-

tion of the bridging carbonyl group appeared at 1754

cm^-1. The ¹³C signals of the carbonyl groups were

observed at δ 205.3 and 260.3, which were assigned to

the terminal and the bridging carbonyl group, respec-

tively. The ²⁹Si signal of 8 appeared at δ 210.7, which

was very similar to that of the dicarbonyl µ-silylene

complex cis-6a .

The mono(µ-silylene) complexes 4b,c also react with

carbon monoxide under forced conditions to afford a

mixture of {Cp*Ru(CO)}(µ-SiREt) (8b, R ) Me; 8c, R

) Ph) and diruthenium tetracarbonyl complex 7. Com-

plexes 8b,c were isolated by means of chromatography

on alumina in 17% and 24% yields, respectively. The

trans geometry of the two CO groups was confirmed on

1

the basis of the H and ¹³C NMR data. The structure of

8c was confirmed by X-ray diffraction studies. An

ORTEP diagram of 8c is depicted in Figure 10, and

selected bond distances and angles are listed in Table

7. Structural parameters of 8c were very similar to

those of 8a , irrespective of the difference in the substit-

uents on the silicon atom.

Rea ction of Bis(µ-silylen e) Com p lexes 5 w ith

Acetylen e. Reaction of the bis(µ-diphenylsilylene) com-

plex 3a with acetylene afforded the disilaruthenacyclo-

pentene complex {Cp*Ru(µ-H)}₂(-SiPh₂CHdCHSiPh₂)

(9) (Scheme 6).^11aThe experiment using deuterated

acetylene proved that the disilaruthenacyclopentene

skeleton was formed by way of insertion of an acetylene

The molecular structure of 8a is shown in Figure 9,

and selected bond distances and angles are listed in

Table 6, respectively. Recrystallization of the crude

mixture from cold pentane afforded a yellow mixed

crystal containing both 7 and 8a in the ratio of 1:2 in

the unit cell. Since 7 has already been structurally

3870 Organometallics, Vol. 22, No. 19, 2003

Takao et al.

As for complex 5, the coordination site for the acety-

lene to insert into the Ru-Si bond has been already

occupied by the phosphine. Therefore, the reactivity of

5 should be different from that of the bis(µ-silylene)

complex 3 as far as the phosphine coordination to the

ruthenium center. Thus, the reaction of 5 with acetylene

was investigated to show the role of the coordination

site of the cis-bis(µ-silylene).

The bis(µ-silylene) complex 5, containing PMe₃on one

ruthenium center, slowly reacted with acetylene at

ambient temperature to yield the vinylidene complex

{Cp*Ru(µ-SiPhMe)}₂(PMe₃)(dCdCH₂) (10) (eq 11). Com-

1

plex 10 was fully characterized by means of the H, ¹³C,

and ²⁹Si NMR, IR, and elemental analysis.

Figu r e 10. Molecular structure of {Cp*Ru(CO)}₂(µ-SiPhEt)-

(µ-CO) (8c), with thermal ellipsoids at the 30% probability

level.

Ta ble 7. Selected Bon d Dista n ces (Å) a n d An gles

(d eg) for 8c

Ru(1)-Ru(2)

Ru(1)-C(1)

Ru(2)-Si(1)

Ru(2)-C(3)

Si(1)-C(6)

C(2)-O(2)

2.848(2)

2.016(2)

2.389(2)

1.844(8)

1.898(7)

1.148(7)

Ru(1)-Si(1)

Ru(1)-C(2)

Ru(2)-C(1)

Si(1)-C(4)

C(1)-O(1)

C(3)-O(3)

2.402(4)

1.857(7)

2.035(2)

1.894(6)

1.184(7)

1.152(7)

Si(1)-Ru(1)-C(1)

Ru(1)-Si(1)-Ru(2)

Ru(1)-C(1)-Ru(2)

Ru(2)-C(1)-O(1)

Ru(2)-C(3)-O(3)

98.7(2)

Si(1)-Ru(2)-C(1)

98.6(2)

101.4(3)

135.5(5)

175.9(6)

72.96(6) C(4)-Si(1)-C(6)

89.3(3)

135.2(5)

173.0(6)

Ru(1)-C(1)-O(1)

Ru(1)-C(2)-O(2)

The ¹³C signals derived from the terminally bound

vinylidene ligand appeared at δ 327.5 (s, C^R) and δ 91.4

(t, J _C-H) 160.2, C^â), respectively. One singlet assign-

able to the vinylidene proton was observed at δ 3.25 in

the ¹H NMR spectrum. The two vinylidene protons were

observed to be equivalent, and this is consistent with

the terminally bound structure of 10. In the IR spectra

into the Ru-Si bond. The reaction most likely proceeds

via an intermediary cis-bis(µ-silylene) complex, in anal-

ogy to the reaction of 3b with PMe₃. In this regard, the

reaction of 3a with acetylene was another example

indicating the existence of the cis-bis(µ-silylene) species

as well as the reaction with PMe₃leading to 5.

Sch em e 6

Bond Cleavage of Tertiary Silanes on Ru₂Centers

Organometallics, Vol. 22, No. 19, 2003 3871

of 10, a strong absorption assignable to ν(CdC) was

the intermediary µ-silyl ligand. The kinetic parameters

for the hydride site exchange are different from those

for the rotation of the µ-silylene ligand, which implied

that the two processes took place independently.

observed at 1593 cm^-1

.

The syn orientation of the two bridging silicon atoms

was confirmed by the fact that the two silicon atoms

were observed to be equivalent in the ²⁹Si NMR spectra.

The ²⁹Si signal of 9 appeared at δ 213.1 as a doublet

signal due to coupling with the ³¹P atom (²J _Si-P) 19.2

Hz). The chemical shift was very close to those of the

µ-silylene complexes containing carbonyl ligands, 6 and

8.

Since a single crystal suitable for the diffraction

studies was not obtained, orientation of the two Cp*

groups was not determined: that is, whether it is cis or

trans with respect to the Ru₂Si₂core. However, complex

10 was tentatively identified as a cis structure from the

analogy to the reaction of 3a with CO, yielding cis-6a .

Since the trimethylphosphine was coordinated on one

ruthenium center, insertion of acetylene into the Ru-

Si bond was inhibited. Although π-coordination of

acetylene was required to form the disilaruthenacycle,

the reaction of 5 with acetylene leading to the vinylidene

complex 10 proceeded by way of C-H bond cleavage of

acetylene concomitant with elimination of the two

hydride ligands. There have been many examples for

the formation of a vinylidene complex via an acetylide

intermediate, and its mechanism has been well eluci-

dated in detail.²⁹

Although the X-ray studies of 3a and 3c showed trans

structures of the bis(µ-silylene) complexes with respect

to the Ru-Ru vector, the cis-bis(µ-silylene) intermediate

was proposed for the hydride site-exchange process on

the basis of the VT-NMR studies as shown in Scheme

3. The reaction of 3b with PMe₃afforded the bis(µ-

silylene) complex 5, whose µ-silylene ligands adopted a

cis form with respect to the Ru-Ru vector. Thus,

formation of 5 strongly implied the transformation of

the bis(µ-silylene) complex from trans to cis in solution.

Such transformation from the trans to cis structure

seems to be the origin of the unique reactivities of the

bis(µ-silylene) complexes. The mono(µ-silylene) complex

4 has a rigid structure in solution and is less reactive

than 3. It is very helpful for understanding the reactiv-

ity of the polyhydride clusters to realize the behavior

of the hydride ligands.

We are now continuing research on the reactivities

of the µ-silylene ligands on the cluster and are especially

focusing on the reactivity of the cis-bis(µ-silylene)

intermediate for the purpose of formation of Si-C and

Si-Si bonds on the cluster.

Con clu sion

Exp er im en ta l Section

Several complexes containing a µ-silylene ligand, 3-6,

8, and 10, have been synthesized in this study. X-ray

diffraction studies revealed that the Ru-Si bonds of

these complexes have similar bond lengths. However,

a remarkable high-field shift of the ²⁹Si signal was

observed only for the bis(µ-silylene) complex 3 in the

²⁹Si NMR studies. Another remarkable property of 3

was its fluxionality; the VT-NMR studies of the mixed-

bridge bis(µ-silylene) complex 3c revealed formation of

a µ-silyl intermediate during the site-exchange reaction

of the hydride ligands. Actually, the chemical shift of δ

110 for 3 is very close to those of the bis(µ-silyl)

complexes 2 containing 2e-3c Ru-H-Si interactions.

Therefore, such a high-field shift of the ²⁹Si signal was

most likely attributed to the contribution of the reso-

nance hybrid of the µ-silyl structure in solution. In

contrast to this, the ²⁹Si signal for the nonfluxional

mono(µ-silylene) complex 4 was observed in the low-

magnetic-field region (ca. δ 260-310), even though 4

contains hydride ligands.

Consideration of the formal oxidation state of the

metal centers is also helpful for understanding the

different properties of the silylene bridges in 3 and 4.

The higher formal oxidation state of 3, which is formally

a Ru(IV)-Ru(IV) species, would facilitate rearrange-

ments involving reductive Si-H bond formation into the

µ-silyl intermediate.

Another important behavior of the µ-silylene ligand

of 3 was the “rotation” around the Ru-Si bonds, which

was seen in the isomerization between 3b-syn and 3b-

a n ti. The VT-NMR studies of 3c also proved rotation

of the bridging silylene ligand. Rotation of the µ-silylene

ligand most likely proceeded by way of a “1,2-shift” of

Gen er a l P r oced u r es. All experiments were carried out

under an argon atmosphere. All compounds were treated with

Schlenk techniques. Reagent grade toluene, Et₂O, and THF

were dried over sodium-benzophenone ketyl and stored under

an argon atmosphere. Pentane and dichloromethane were

dried over phosphorus pentoxide and stored under an argon

atmosphere. Benzene-d₆, toluene-d₈, and THF-d₈were dried

over sodium-benzophenone ketyl and stored under an argon

atmosphere. Phenylvinylsilane and methylvinylsilane were

synthesized by the reduction of the corresponding chlorolvi-

nylsilane by LiAlH₄in diethyl ether. Triphenylsilane, diphe-

nylmethylsilane, phenyldimethylsilane, phenyltrimethylsilane,

and other substrates were used as received. IR spectra were

1

recorded on a J ASCO FT/IR-5000 spectrophotometer. H and

¹³C NMR spectra were recorded on J EOL GX-500, Varian

Gemini-3000, and Varian INOVA-400 Fourier transform spec-

trometers with tetramethylsilane as an internal standard.

Variable-temperature ¹H NMR spectra were recorded on a

Varian INOVA-400. ²⁹Si NMR spectra were recorded on J EOL

EX-270 and Varian INOVA-400 instruments with tetrameth-

ylsilane as an external standard. Field-desorption mass spectra

were recorded on a Hitachi GC-MS M80 high-resolution mass

spectrometer. Elemental analyses were performed by the

Analytical Facility at the Research Laboratory of Resources

Utilization, Tokyo Institute of Technology. The dinuclear

ruthenium tetrahydride complex (η⁵-C₅Me₅)Ru(µ-H)₄Ru(η⁵-C₅-

Me₅) (1) was prepared according to a previously published

method.¹³

X-r a y Da ta Collection a n d Red u ction . X-ray-quality

crystal of 3c, 4a ,b, 5, and 8a ,c were obtained directly from

the preparations described below and mounted on glass fibers.

Diffraction experiments were performed on a Rigaku AFC-5R

four-circle diffractometer with graphite-monochromated Mo

KR radiation (λ ) 0.710 69 Å) at 23 °C. Intensity data were

collected using a ω/2θ scan technique; three standard reflec-

tions were recorded every 150 reflections. The data for 4b and

8a ,c were processed using the TEXSAN crystal solution

(29) Bruce, M. I. Chem. Rev. 1991, 91, 197-257.

3872 Organometallics, Vol. 22, No. 19, 2003

Takao et al.

package³⁰operating on an IRIS Indigo computer, and the data

for 3c, 4a , and 5 were processed using the SHELX-97

programs.³¹Neutral atom scattering factors were obtained

from the standard sources.³²In the reduction of the data,

Lorentz/polarization corrections and empirical adsorption cor-

rections based on azimuthal scans were applied to the data

for each structure.

Str u ctu r e Solu tion a n d Refin em en t for 4b, 8a ,c. The

Ru atom positions were determined using direct methods

employing the MITHRIL-90³³and SAPI-91³⁴direct-methods

routines for 4b, and 8a ,c, respectively. In each case the

remaining non-hydrogen atoms were located from successive

difference Fourier map calculations using the DIRDIF-92

programs.³⁵In both cases the non-hydrogen atoms were refined

anisotropically by using full-matrix least-squares techniques

on F. In the case of 4b, the positions of hydrogen atoms bonded

to the Ru were located by sequential difference Fourier

syntheses and were refined isotropically. Crystal data and

results of the analyses are listed in Table 8.

The funnel was charged with triphenylsilane (0.133 g, 0.51

mmol) and THF (10 mL). The Ph₃SiH solution was then slowly

added dropwise to the solution of 1 for 5 h. The solution was

stirred for 10 h at 25 °C. The solution turned dark red. The

solvent was then removed under reduced pressure. Red

residual oil containing the bis(µ-diphenylsilylene) complex

{Cp*Ru(µ-SiPh₂)(µ-H)}₂(3a ), the mono(µ-diphenylsilylene)

complex {Cp*Ru(µ-H)}₂(µ-SiPh₂) (4a ), and the remaining

triphenylsilane was obtained. After the remaining silane was

removed by rinsing with 5 mL of pentane three times, 0.146 g

of a red solid including 3a and 4a was obtained. The ratio

between 3a and 4a was estimated at 1:2 by means of ¹H NMR

spectroscopy. The residual solid was then dissolved in toluene

(15 mL). The solution was transferred to a glass autoclave

pressurized with 7 atm of H₂. After the solution was stirred

for 30 h at 25 °C, the solvent was removed under reduced

pressure. The residual solid was washed seven times with 5

mL of pentane to remove the bis(µ-diphenylsilyl) complex

{Cp*Ru(µ-η²-HSiPh₂)}(µ-H)(H) (2a ). An 80.2 mg amount of

complex 4a was obtained as a dark red solid (56% yield).

Bis(µ-d ip h en ylsilylen e) Com p lex {Cp *Ru (µ-SiP h ₂)(µ-

H)}₂(3a ). ¹H NMR (270 MHz, 23 °C, toluene-d₈): δ -19.69

(s, 2H, RuH), 1.40 (s, 30H, Cp*), 7.9-7.2 (m, 20H, Ph). ¹³C

NMR (68 MHz, 23 °C, benzene-d₆): δ 10.8 (q, J _C-H) 127.0

Hz, C₅Me₅), 90.9 (s, C₅Me₅), 127.3 (d, J _C-H) 157.8 Hz, Ph),

Str u ctu r e Solu tion a n d Refin em en t for 3c, 4a , a n d 5.

The structure was solved by direct methods using SHELXS-

97^31aand refined by full-matrix least-squares techniques on

F²with SHELXL-97.^31bAll hydrogen atoms were located by

difference Fourier maps and refined isotropically, while all

non-hydrogen atoms were refined anisotropically. Crystal data

and results of the analyses are listed in Table 8.

137.6 (d, J _C-H) 156.8 Hz, Ph), 145.9 (s, Ph ipso), one ¹³C signal

29

of the phenyl group was obscured by the solvent signals.

-

Va r ia ble-Tem p er a tu r e NMR Sp ectr a a n d Dyn a m ic

NMR Sim u la tion s. Variable-temperature NMR studies were

performed in flame-sealed NMR tubes in THF-d₈for 3b-syn /

a n ti and toluene-d₈for 3c using a Varian INOVA-400 Fourier

transform spectrometer with tetramethylsilane as an internal

standard. NMR simulations for the hydride ligands of 3b-syn

and 3c were performed using gNMR v4.1.0 (1995-1999 Ivory

Soft). In the case of 3c, simulations for the methyl groups on

the bridging silicon atom were also performed. The ¹H-¹H

coupling constants between the hydride ligands were esti-

mated at J _H-H) 6.12 Hz for 3b-syn and J _H-H) 6.00 Hz for

Si{¹H} NMR (54 MHz, 60 °C, benzene-d₆): δ 109.8. IR (KBr,

cm^-1): 3060, 2984, 2910, 1580, 1480, 1429, 1379, 1091, 1031,

732, 699, 512. FD-MS: m/e 840. The field desorption mass

spectrum was measured, and the intensities of the obtained

isotopic peaks for C₄₄H₅₂Ru₂Si₂agreed with the calculated

value within experimental error.

Mon o(µ-d ip h en ylsilylen e) Com p lex {Cp *Ru (µ-H)}₂(µ-

SiP h ₂) (4a ). ¹H NMR (500 MHz, 23 °C, THF-d₈): δ -13.51 (s,

2H, RuH), 1.56 (s, 30H, Cp*), 8.3-7.3 (m, 10H, Ph). ¹³C{¹H}

NMR (75 MHz, 23 °C, THF-d₈): δ 11.3 (C₅Me₅), 87.3 (C₅Me₅),

128.1 (Ph), 129.3 (Ph), 138.2 (Ph). ²⁹Si{¹H} NMR (54 MHz, 23

°C, benzene-d₆): δ 265.0. IR (KBr, cm^-1): 3062, 2982, 2904,

1480, 1428, 1382, 1093, 1032, 738, 700. FD-MS: m/e 658. The

field desorption mass spectrum was measured, and the inten-

sities of the obtained isotopic peaks for C₃₂H₄₂Ru₂Si agreed

with the calculated value within experimental error. Anal.

Calcd for C₃₂H₄₂Ru₂Si: C, 58.51; H, 6.44. Found: C, 58.14; H,

6.33.

3c, respectively. The coupling constants between the hydrides

2

and the bridging silicon ligand were estimated at J _Si-H

)

7.20-9.00 Hz from the line shapes of satellite signals around

the resonance of the hydride ligands. Final simulated line

shapes were obtained via an iterative parameter search upon

the exchange constant k. Full details of the fitting procedure

may be found in the Supporting Information. The rate con-

stants k that accurately modeled the experimental spectra at

each temperature are given in Figure 1. The activation

parameters ∆H^qand ∆S^qwere determined from the plot of ln-

(k/T) versus 1/T. Estimated standard deviations (σ) in the slope

and y intercept of the Eyring plot determined the error in ∆H^q

and ∆S^q, respectively. The standard deviation in ∆G^qwas

determined from the formula σ(∆G^q)²) σ(∆H^q)²+ [T(σ(∆S^q))]²

-2T(σ(∆H^q))[σ(∆S^q)].

Rea ction of Cp *Ru (µ-H)₄Ru Cp * (1) w ith P h ₂MeSiH. A

50 mL flask was charged with toluene (20 mL) and Cp*Ru(µ-

H)₄RuCp* (1; 0.317 g, 0.67 mmol). After 2.5 molar equiv of

diphenylmethylsilane (0.34 mL, 1.68 mmol) was added with

vigorous stirring, the solution was allowed to react for 12 h at

25 °C. The solvent was then removed under reduced pressure,

and the residue was washed two times with 5 mL of methanol

to remove the remaining silane. The dark red residual solid

was dissolved in 2 mL of toluene, and the product was purified

by the use of column chromatography on neutral alumina

(Merck Art. 1097) with hexane/toluene. Removal of the solvent

under reduced pressure afforded 0.397 g of a mixture of

diastereomers of the bis(µ-phenylmethylsilylene) complex

{Cp*Ru(µ-SiPhMe)(µ-H)}₂(3b-syn / a n ti) as an orange solid

(84%). The ratio between 3b-syn and 3b-a n ti was estimated

Rea ction of Cp *Ru (µ-H)₄Ru Cp * (1) w ith P h ₃SiH. A 50

mL flask equipped with a dropping funnel was charged with

THF (10 mL) and Cp*Ru(µ-H)₄RuCp* (1; 0.105 g, 0.22 mmol).

(30) TEXSAN: Crystal Structure Analysis Package; Molecular

Structure Corp., The Woodlands, TX, 1985 and 1992.

(31) (a) Sheldrick, G. M. SHELXS-97: Program for Crystal Structure

Solution, University of Go¨ttingen, Go¨ttingen, Germany, 1997. (b)

Sheldrick, G. M., SHELXL-97: Program for Crystal Structure Solution;

University of Go¨ttingen, Go¨ttingen, Germany, 1997.

(32) International Tables for X-ray Crystallography; Kynoch

Press: Birmingham, U.K., 1975; Vol. 4.

1

as 55:45 on the basis of ¹H NMR spectra. H NMR (400 MHz,

60 °C, THF-d₈): 3b-syn , δ -20.4 (br, 2H, RuH), 1.08 (s, 6H,

SiMe), 1.529 (s, 30H, Cp*), 7.0-7.5 (m, 10H, Ph); 3b-a n ti, δ

-20.44 (s, 2H, RuH), 1.12 (s, 6H, SiMe), 1.527 (s, 30H, Cp*),

(33) Gilmore, C. J . MITHRIL 90: MITHRIL-An Integrated Direct

Methods Computer Program; University of Glasgow, Glasgow, Scot-

land, 1990.

1

7.0-7.5 (m, 10H, Ph). H NMR (400 MHz, -40 °C, THF-d₈):

3b-syn , δ -21.01 (d, J _H-H) 6.1 Hz, 1H, RuH), -19.77 (d, J _H-H

) 6.1 Hz, 1H, RuH), 1.05 (s, 6H, SiMe), 1.50 (s, 30H, Cp*),

6.9-7.8 (m, 10H, Ph); 3b-a n ti, δ -20.44 (s, 2H, RuH), 1.09

(s, 6H, SiMe), 1.50 (s, 30H, Cp*), 7.0-7.5 (m, 10H, Ph). ¹³C-

{¹H} NMR (125 MHz, 23 °C, benzene-d₆): δ 5.7 (SiMe), 5.8

(SiMe), 11.5 (C₅Me₅), 11.6 (C₅Me₅), 90.06 (C₅Me₅), 90.10 (C₅-

(34) Fan, H.-F. SAPI91: Structure Analysis Programs with Intel-

ligent Control; Rigaku Corp., 1991.

(35) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;

Garcia-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C.

DIRDIF92: The DIRDIF Program System; Technical Report of the

Crystallography Laboratory; University of Nijmegen, Nijmegen, The

Netherlands, 1992.

Bond Cleavage of Tertiary Silanes on Ru₂Centers

Organometallics, Vol. 22, No. 19, 2003 3873

Ta ble 8. Cr ysta llogr a p h ic Da ta

(a) Compounds 4b and 8a ,c

4b

8a + 0.5 7

8c

Crystal Parameters

formula

cryst syst

space group

a, Å

b, Å

c, Å

R, deg

â, deg

γ, deg

V, Å³

C

₂₃H₄₀Ru₂Si

C₄₇H₅₅O₅Ru₃Si

triclinic

P1h

C₃₁H₄₀O₃Ru₂Si

monoclinic

P2₁/n

9.464(4)

16.327(2)

20.021(4)

monoclinic

P2₁

10.365(3)

14.220(4)

8.651(2)

11.197(4)

18.943(5)

10.954(2)

99.39(2)

90.02(2)

75.51(2)

2217(1)

2

104.07(2)

96.69(3)

1236.7(6)

2

1.468

3072(1)

4

1.493

Z

D

_calcd, g cm^-3

1.544

temp, °C

25

12.75

0.15 × 0.10 × 0.10

23

10.80

0.20 × 0.10 × 0.05

23

10.51

0.30 × 0.25 × 0.20

µ(Mo KR), cm^-1

cryst dimens, mm

Data Collection

diffractometer

radiation

monochromator

scan type

Rigaku AFC-5R

Mo KR (λ ) 0.710 69 Å)

graphite

ω/2θ

2θ_max, deg

55.0

16.0

3145

2959

50.0

16.0

5541

5182

scan speed, deg min^-1

no. of rflns collected

no. of indep data

no. of indep data obsd

16.0

8243

7809

3290 (I > 3σ)

2246 (I > 3σ)

3130 (I > 3σ)

Refinement

R

R_w

0.031

0.024

0.00

234

0.056

0.046

0.03

505

0.036

0.030

0.03

334

p factor

no. of variables

GOF

2.36

1.49

1.33

(b) Compounds 3c, 4a , and 5

3c

4a

5

Crystal Parameters

formula

cryst syst

space group

a, Å

b, Å

c, Å

R, deg

â, deg

γ, deg

V, Å³

C

₂₉H₄₆Ru₂Si₂

C

₃₂H₄₂Ru₂Si

C₃₇H₅₇PRu₂Si₂

monoclinic

P2₁/n

11.242(10)

18.453(11)

18.065(7)

triclinic

P1h

triclinic

P1h

14.602(3)

18.901(3)

11.238(4)

94.45(2)

90.57(2)

99.325(16)

3050.6(13)

4

11.896(2)

12.345(2)

10.972(1)

102.21(1)

110.744(9)

85.23(1)

1472.8(3)

2

92.09(5)

3745(4)

4

1.403

Z

D

_calcd, g cm^-3

1.422

1.481

temp, °C

23

10.83

0.20 × 0.15 × 0.10

23

10.84

0.30 × 0.10 × 0.10

23

9.37

µ(Mo KR), cm^-1

cryst dimens, mm

0.10 × 0.15 × 0.10

Data Collection

diffractometer

radiation

monochromator

scan type

Rigaku AFC-5R

Mo KR (λ ) 0.710 69 Å)

graphite

ω/2θ

50.0

2θ_max, deg

scan speed, deg min^-1

no. of rflns collected

no. of indep data

no. of indep data obsd

16.0

11 201

10 727

6695 (I > 2σ)

5449

5178

4356 (I > 2σ)

7189

6825

4267 (I > 2σ)

Refinement

R1 [I > 2σ]

wR2 [I > 2σ]

no. of params

GOF on F²

0.0432

0.1017

625

0.0355

0.0952

324

0.0606

0.1440

402

1.002

1.055

1.008

Me₅), 126.9 (SiPh), 127.33 (SiPh), 127.38 (SiPh), 136.9 (SiPh),

149.2 (SiPh-ipso), 149.8 (SiPh-ipso). Assignment of these ¹³C

signals to syn and anti was omitted, and some of these signals

for the phenyl carbons were not observed due to obstruction

by the solvent signals. ²⁹Si{¹H} NMR (54 MHz, 23 °C, benzene-

d₆): δ 108.2, 107.7 (3b-syn and/or 3b-a n ti). IR (KBr, cm^-1):

3062, 2962, 2896, 1481, 1427, 1263, 1121, 1091, 1070, 780, 748,

698. FD-MS: m/e 716. The field desorption mass spectrum was

3874 Organometallics, Vol. 22, No. 19, 2003

Takao et al.

measured, and the intensities of the obtained isotopic peaks

for C₃₄H₄₈Ru₂Si₂agreed with the calculated value within

experimental error.

ing silane was removed by rinsing with 5 mL of pentane three

times, 4c was obtained as a red solid (0.185 g, 0.34 mmol, 28%

yield). ¹H NMR (300 MHz, 23 °C, benzene-d₆): δ -14.69 (d,

J _H-H) 3.7 Hz, 1H, RuH), -14.60 (d, J _H-H) 3.7 Hz, 1H, RuH),

1.32 (s, 3H, SiCH₃), 1.43 (q, J _H-H) 7.7 Hz, 2H, SiCH₂), 1.71

(t, J _H-H) 7.4 Hz, 3H, SiCH₂CH₃), 1.77 (s, 30H, Cp*). ¹³C NMR

(75 MHz, 23 °C, benzene-d₆): δ 11.6 (q, J _C-H) 123.4 Hz,

Rea ction of Cp *Ru (µ-H)₄Ru Cp * (1) w ith P h Me₂SiH. A

50 mL flask was charged with toluene (10 mL) and Cp*Ru(µ-

H)₄RuCp* (1; 0.149 g, 0.31 mmol). The flask was cooled at -78

°C with dry ice/methanol bath. After 2.5 molar equiv of

phenyldimethylsilane (0.12 mL, 0.78 mmol) was added with

vigorous stirring, the solution was allowed to react for 2 h at

0 °C with argon bubbling. The solvent and remaining silane

were removed under reduced pressure, and 0.212 g of a

residual solid including the bis(µ-silylene) complexes {Cp*Ru-

SiCH₂CH₃), 11.8 (q, J _C-H) 126.6 Hz, C₅Me₅), 17.5 (q, J _C-H

)

118.8 Hz, SiCH₃), 24.3 (t, J _C-H) 116.6 Hz, SiCH₂CH₃), 85.8

(s, C₅Me₅). ²⁹Si{¹H} NMR (54 MHz, 23 °C, benzene-d₆):

δ

310.8. IR (KBr, cm^-1): 2980, 2960, 2896, 1477, 1402, 1379,

1226, 1031, 785, 679, 623. Anal. Calcd for C₂₃H₄₀Ru₂Si: C,

50.52; H, 7.37. Found: C, 50.91; H, 7.39.

1

(µ-H)}₂(µ-SiPhMe)(µ-SiMe₂) (3c; >95% based on H NMR) and

1

{Cp*Ru(µ-H)(µ-SiMe₂)}₂(3d ; <2% based on H NMR) and their

P r ep a r a tion of {Cp *Ru (µ-SiP h Me)}₂(P Me₃)(H)₂(5). A

50 mL flask was charged with toluene (10 mL) and {Cp*Ru-

(µ-SiPhMe)(µ-H)}₂(3b-syn /a n ti) (0.222 g, 0.31 mmol). After

2.5 molar equiv of trimethylphosphine (1.58 M/toluene; 0.5 mL,

0.79 mmol) was added with vigorous stirring, the reaction

mixture was stirred for 24 h at 25 °C. The solution turned

from dark red to orange. After the solvent and remaining PMe₃

were removed under reduced pressure, a yellow residual solid

was obtained. This solid was dissolved in 5 mL of pentane,

and the product was purified by the use of filtration on Celite.

Removal of the solvent in vacuo afforded 0.200 g of 5 as a

hydrogenated bis(µ-silyl) complexes was obtained. Analytically

pure 3c was obtained from a cold pentane solution of the

mixture as a dark red microcrystal.

{Cp *Ru (µ-H)}₂(µ-SiP h Me)(µ-SiMe₂) (3c). ¹H NMR (400

MHz, 70 °C, THF-d₈): δ -20.80 (s, 2H, RuH), 0.79 (br, 3H,

SiMe₂), 0.83 (br, 3H, SiMe₂), 1.01 (s, 3H, SiMePh), 1.68 (s, 30H,

1

Cp*), 7.0-7.3 (m, 5H, SiMePh). H NMR (400 MHz, -60 °C,

THF-d₈): δ -21.13 (d, J _H-H) 6.0 Hz, 1H, RuH), -20.44 (d,

J _H-H) 6.0 Hz, 1H, RuH), 0.74 (s, 3H, SiMe₂), 0.79 (br, 3H,

SiMe₂), 0.97 (s, 3H, SiMePh), 1.65 (s, 30H, Cp*), 6.7-7.7 (m,

5H, SiMePh). ¹³C{¹H} NMR (75 MHz, 23 °C, benzene-d₆): δ

5.5 (SiMe), 9.8 (SiMe), 10.0 (SiMe), 11.8 (C₅Me₅), 90.1 (C₅Me₅),

137.2 (br, Ph), 149.9 (Ph-ipso). ²⁹Si{¹H} NMR (54 MHz, 23 °C,

benzene-d₆): δ 112.3 (SiMe₂), 107.9 (SiPhMe). FD-MS: m/e

654. The field desorption mass spectrum was measured, and

the intensities of the obtained isotopic peaks for C₂₉H₄₆Ru₂Si₂

agreed with the calculated value within experimental error.

Anal. Calcd for C₂₉H₄₆Ru₂Si₂: C, 53.34; H, 7.10. Found: C,

51.45; H, 6.90.

1

yellow solid (82% yield). H NMR (500 MHz, 23 °C, toluene-

d₈): δ -13.06 (s, 2H, RuH), 1.01 (d, J _P-H) 1.2 Hz, 6H, SiMe),

1.20 (d, J _P-H) 0.7 Hz, 15H, Cp*), 1.5-1.1 (br, 9H, PMe₃), 1.84

(s, 15H, Cp*), 7.3-8.3 (m, 10H, SiPh). ¹H NMR (500 MHz, -40

°C, toluene-d₈): δ -12.99 (s, 2H, RuH), 1.02 (s, 6H, SiMe), 1.11

(d, J _P-H) 7.9 Hz, 3H, PMe), 1.18 (s, 15H, Cp*), 1.35 (d, J _P-H

) 7.9 Hz, 3H, PMe), 1.80 (s, 15H, Cp*), 7.3-8.4 (m, 10H, SiPh).

¹³C{¹H} NMR (75 MHz, 23 °C, benzene-d₆): δ 11.2 (C₅Me₅),

11.8 (C₅Me₅), 19.0 (d, J _P-C) 1.4 Hz, SiMe), 25.7 (br, PMe),

94.7 (C₅Me₅), 94.8 (C₅Me₅), 127.1 (SiPh), 127.4 (SiPh), 136.5

(SiPh), 155.2 (SiPh-ipso). ²⁹Si{¹H} NMR (54 MHz, 23 °C,

benzene-d₆): δ 205.2 (d, J _P-Si) 20.5 Hz). ³¹P{¹H} NMR (109

MHz, 23 °C, benzene-d₆): δ 16.6. IR (KBr, cm^-1): 3128, 3040,

3000, 2960, 2904, 2856, 2720, 2036 (ν(Ru-H)), 1957, 1889,

1827, 1580, 1562, 1425, 1377, 1276, 1261, 1083, 1025, 944, 779,

735. Anal. Calcd for C₃₇H₅₇PRu₂Si₂: C, 56.17; H, 7.26. Found:

C, 56.16; H, 7.51.

Th er m olysis of {Cp *R u (µ-SiP h Me)}₂(P Me₃)(H )₂(5).

Complex 5 (10 mg, 0.013 mmol) was dissolved in benzene-d₆

(0.3 mL), and then the solution was charged in an NMR tube.

The NMR tube was then heated at 100 °C for 10 h. The ¹H

NMR spectrum revealed complete disappearance of 5 and

formation of a mixture of 3b-syn / a n ti and trimethylphosphine

(δ 0.83, J _P-H) 12.8 Hz).

Rea ction of {Cp *Ru (µ-SiP h ₂)(µ-H)}₂(3a ) w ith H₂. Tolu-

ene (20 mL) and complex 3a (0.125 g, 0.15 mmol) was charged

in a 100 mL flask under 1 atm of H₂. After the solution was

stirred for 48 h at 25 °C, the solution turned orange. The bis-

(µ-diphenylsilyl) complex {Cp*Ru(µ-η²-HSiPh₂)}₂(µ-H)(H) (2a )

was obtained as an orange solid by the removal of the solvent

under reduced pressure (0.125 g, 100% yield). ²⁹Si{¹H} NMR

(54 MHz, 23 °C, benzene-d₆): δ 95.1.

Rea ction of {Cp *Ru (µ-SiP h Me)(µ-H)}₂(3b-syn /a n ti)

w ith H₂. Toluene (10 mL) and a mixture of 3b-syn and 3b-

a n ti (0.155 g, 0.22 mmol) was charged in a 100 mL flask under

1 atm of H₂. After the solution was stirred for 8 h at 25 °C,

the solution turned orange. A mixture of bis(µ-phenylmethyl-

silyl) complexes {Cp*Ru(µ-η²-HSiPhMe)}₂(µ-H)(H) (2b-syn /

a n ti) was obtained as a yellow solid by removal of the solvent

under reduced pressure (0.155 g, 100% yield).

{Cp *Ru (µ-H)(µ-SiMe₂)}₂(3d ). ¹H NMR (400 MHz, -60 °C,

THF-d₈): δ -21.16 (s, 2H, RuH), 0.66 (s, 12H, SiMe), 1.78 (s,

30H, Cp*). FD-MS: m/e 594. The field desorption mass

spectrum was measured, and the intensities of the obtained

isotopic peaks for C₂₄H₄₆Ru₂Si₂agreed with the calculated

value within experimental error.

P r ep a r a tion of {Cp *Ru (µ-H)}₂(µ-SiP h Et) (4b). A 50 mL

flask equipped with a dropping funnel was charged with

toluene (20 mL) and Cp*Ru(µ-H)₄RuCp* (1; 0.665 g, 1.39

mmol). The funnel was charged with phenylvinylsilane (0.525

mL, 0.51 mmol) and toluene (25 mL). The PhSi(CHdCH₂)H₂

solution was then slowly added dropwise to the solution of 1

for 1 h. The solution was stirred for 1 h at 25 °C. The solvent

was then removed under reduced pressure. After the remain-

ing silane was removed by rinsing with 5 mL of pentane three

times, 4b was obtained as a red solid (0.570 g, 0.94 mmol, 67%

yield). ¹H NMR (500 MHz, 23 °C, benzene-d₆): δ -13.43 (d,

J _H-H) 3.9 Hz, 1H, RuH), -13.41 (d, J _H-H) 3.9 Hz, 1H, RuH),

1.66 (s, 30H, Cp*), 1.70 (q, J _H-H) 7.4 Hz, 2H, SiCH₂), 1.83 (t,

J _H-H) 7.4 Hz, 3H, SiCH₂CH₃), 7.3-8.4 (m, 5H, SiPh). ¹³C

NMR (125 MHz, 23 °C, benzene-d₆): δ 11.0 (q, J _C-H) 124.0

Hz, SiCH₂CH₃), 11.6 (q, J _C-H) 126.5 Hz, C₅Me₅), 18.1 (t, J _C-H

) 115.4 Hz, SiCH₂CH₃), 86.2 (s, C₅Me₅), 127.5 (Ph), 128.8 (Ph),

136.4 (Ph), 150.1 (Ph-ipso). ²⁹Si{¹H} NMR (54 MHz, 23 °C,

benzene-d₆): δ 291.7. IR (KBr, cm^-1): 2980, 2956, 2900, 1479,

1431, 1383, 1094, 1038, 692. FD-MS: m/e 610. The field

desorption mass spectrum was measured, and the intensities

of the obtained isotopic peaks for C₂₈H₄₂Ru₂Si agreed with the

calculated value within experimental error. Anal. Calcd for

C

₂₈H₄₂Ru₂Si: C, 55.24; H, 6.95. Found: C, 55.25; H, 7.22.

P r ep a r a tion of {Cp *Ru (µ-H)}₂(µ-SiMeEt) (4c). A 50 mL

flask equipped with a dropping funnel was charged with

toluene (30 mL) and Cp*Ru(µ-H)₄RuCp* (1) (0.581 g, 1.22

mmol). The funnel was charged with methylvinylsilane (0.286

mL, 2.68 mmol) and toluene (40 mL). The MeSi(CHdCH₂)H₂

solution was then slowly added dropwise to the solution of 1

for 3.5 h. The solution was stirred for 2 h at 25 °C. The solvent

was then removed under reduced pressure. After the remain-

Isola tion of 2b-syn . The product was extracted with seven

5 mL portions of pentane, and the combined extract was

evaporated. The yellow residual solid was then dissolved in 3

mL of toluene and purified by the use of column chromatog-

raphy on neutral silica gel (Merck Art. 7734) and alumina

(Merck Art. 1097) with hexane. Removal of the solvent under

reduced pressure afforded 2b-syn as a yellow solid (0.065 g,

Bond Cleavage of Tertiary Silanes on Ru₂Centers

Organometallics, Vol. 22, No. 19, 2003 3875

42% yield). ¹H NMR (500 MHz, -80 °C, THF-d₈): δ -15.17

(s, 1H, RuHRu or RuH), -12.89 (s, 2H, RuHSi), -12.15 (s, 1H,

RuHRu or RuH), 0.66 (s, 6H, SiMe), 2.00 (s, 15H, Cp*), 2.04

(s, 15H, Cp*), 7.0-7.3 (m, 10H, SiPh). ¹³C NMR (126 MHz, 30

°C, THF-d₈): δ 11.1 (q, J _C-H) 120.2 Hz, SiCH₃), 13.7 (q, J _C-H

) 126.3, C₅Me₅), 95.6 (s, C₅Me₅), 128.5 (d, J _C-H) 150.7 Hz,

SiPh), 128.6 (d, J _C-H) 163.1 Hz, SiPh), 135.8 (d, J _C-H) 157.4

Hz, SiPh), 151.2 (s, SiPh-ipso). ²⁹Si{¹H} NMR (54 MHz, 23 °C,

benzene-d₆): δ 101.9. IR (KBr, cm^-1): 3068, 2956, 2908, 2064

(ν(Ru-H)), 1944, 1882, 1814, 1748 br (ν(Ru-H-Si)), 1425,

1377, 1230, 1094, 1029, 787, 733, 698, 673. FD-MS: m/e 718.

The field desorption mass spectrum was measured, and the

intensities of the obtained isotopic peaks for C₃₄H₅₀Ru₂Si₂

agreed with the calculated value within experimental error.

Anal. Calcd for C₃₄H₅₀Ru₂Si₂: C, 56.95; H, 7.03. Found: C,

57.53; H, 6.91.

were charged in a glass autoclave with 5 atm of carbon

monoxide. The solution was stirred for 20 h at 25 °C. The

solution turned bright yellow from dark red. Removal of the

solvent under reduced pressure afforded 34.0 mg of cis-6a as

a yellow solid (100% yield). ¹H NMR (270 MHz, 23 °C,

dichloromethane-d₂): δ 1.52 (s, 30H, Cp*), 7.0-7.7 (m, 20H,

SiPh). ¹³C NMR (68 MHz, 23 °C, dichloromethane-d₂): δ 10.7

(q, J _C-H) 127.0 Hz, C₅Me₅), 99.0 (s, C₅Me₅), 126.7 (d, J _C-H

)

156.7 Hz, SiPh), 127.3 (d, J _C-H) 154.7 Hz, SiPh), 127.7 (d,

J _C-H) 158.9 Hz, SiPh), 128.3 (d, J _C-H) 158.8 Hz, SiPh), 135.2

(d, J _C-H) 158.8 Hz, SiPh), 147.6 (s, SiPh-ipso), 152.2 (s, SiPh-

ipso), 205.2 (s, CO). ²⁹Si{¹H} NMR (54 MHz, 23 °C, benzene-

d₆): δ 211.4. IR (KBr, cm^-1): 3046, 2970, 2910, 1955 (ν(CO)),

1922 sh, 1480, 1425, 1380, 1263, 1078, 1019, 807, 701. FD-

MS: m/e 894. The field desorption mass spectrum was

measured, and the intensities of the obtained isotopic peaks

for C₄₆H₅₀O₂Ru₂Si₂agreed with the calculated value within

experimental error. Anal. Calcd for C₄₆H₅₀O₂Ru₂Si₂: C, 61.86;

H, 5.64. Found: C, 61.63; H, 5.59.

Isola tion of 2b-a n ti. The product was washed by 5 mL of

pentane seven times. Decantation and removal of the solvent

under reduced pressure afforded 2b-a n ti as a yellow solid

1

(0.045 g, 30% yield). H NMR (500 MHz, -80 °C, THF-d₈): δ

P r ep a r a tion of {Cp *Ru (µ-SiP h Me)(CO)}₂(6b). Toluene

(10 mL) and {Cp*Ru(µ-SiPhMe)(µ-H)}₂(3b-syn /a n ti; 0.101 g,

0.14 mmol) were charged in a glass autoclave with 5 atm of

carbon monoxide. The solution was stirred for 20 h at 25 °C.

The solution turned bright yellow from dark red. Removal of

the solvent under reduced pressure afforded a yellow residual

oil containing cis-6b-syn , tr a n s-6b-a n ti, {Cp*Ru(CO)(µ-CO)}₂

(7), and other unidentified byproducts. The complex cis-6b-

syn was extracted with five 5 mL portions of pentane to

remove 7, and the combined extract was purified by the use

of column chromatography on silica gel (Merck Art. 7734) with

hexane/toluene after condensation. Removal of the solvent in

vacuo afforded cis-6b-syn as a yellow solid (0.075 g, 70% yield).

¹H NMR (300 MHz, 23 °C, benzene-d₆): δ 1.36 (s, 30H, Cp*),

1.55 (s, 6H, SiMe), 7.2-7.5 (m, 10H, SiPh). ¹³C{¹H} NMR (68

MHz, 23 °C, benzene-d₆): δ 6.2 (SiMe), 9.0 (C₅Me₅), 96.7 (s,

C₅Me₅), 135.7 (SiPh), 152.0 (SiPh-ipso), 205.6 (s, CO). IR (KBr,

cm^-1): 3064, 2962, 2896, 1932 (ν(CO)), 1903 sh, 1431, 1379,

1265, 1094, 1021, 789. Anal. Calcd for C₃₆H₄₆O₂Ru₂Si₂: C,

56.22; H, 6.03. Found: C, 55.84; H, 6.22. The complex tr a n s-

6b-a n ti was obtained as a yellow microcrystal by recrystal-

lization of the dilute pentane solution of the mixture at -20

°C (0.015 mg, 14%). ¹H NMR (300 MHz, 23 °C, benzene-d₆): δ

1.41 (s, 6H, SiMe), 1.58 (s, 30H, Cp*), 7.2-8.0 (m, 10H, SiPh).

¹³C{¹H} NMR (68 MHz, 23 °C, benzene-d₆): δ 10.6 (C₅Me₅),

11.9 (SiMe), 96.7 (s, C₅Me₅), 127.1 (SiPh), 128.2 (SiPh), 135.6

(SiPh), 149.2 (SiPh-ipso), 205.5 (CO). IR (KBr, cm^-1): 2898,

1899 (ν(CO)), 1477, 1427, 1379, 1261, 1236, 1087, 1029, 793.

P r ep a r a t ion of {Cp *R u (CO)}(µ-SiP h Me)(µ-SiMe₂)

(tr a n s-6c). Toluene (10 mL) and {Cp*Ru(µ-H)}₂(µ-SiPhMe)-

(µ-SiMe₂) (3c; 0.145 g, 0.22 mmol) were charged in a glass

autoclave with 5 atm of carbon monoxide. The solution was

stirred for 5 h at 120 °C. The solution turned bright yellow

from red. Removal of the solvent under reduced pressure

afforded a yellow residual oil containing tr a n s-6c, {Cp*Ru-

(CO)(µ-CO)}₂(7), and other unidentified byproducts. The

products were dissolved in 4 mL of pentane and purified by

the use of column chromatography on neutral alumina (Merck

Art. 1097) with hexane. Removal of the solvent in vacuo

afforded tr a n s-6c as a yellow solid (0.046 g, 37% yield). ¹H

NMR (300 MHz, 23 °C, benzene-d₆): δ 1.08 (s, 3H, SiMe), 1.14

(s, 3H, SiMe), 1.34 (s, 3H, SiMe), 1.61 (s, 15H, Cp*), 1.74 (s,

15H, Cp*), 7.2-8.0 (m, 5H, SiPh). IR (KBr, cm^-1): 2978, 2908,

1903 (ν(CO)), 1479, 1427, 1379, 1263, 1236, 1089, 1071, 841,

793, 768, 663.

-14.98 (br, 1H, RuH), -13.45 (br, 1H, RuH), -13.07 (br, 1H,

RuH), -12.42 (br, 1H, RuH), 0.34 (s, 3H, SiMe), 0.66 (s, 3H,

SiMe), 1.84 (br, 15H, Cp*), 1.93 (br, 15H, Cp*), 7.1-7.7 (m,

10H, SiPh). ¹³C{¹H} NMR (126 MHz, -50 °C, THF-d₈): δ 8.3

(SiMe), 10.5 (SiMe), 12.4 (C₅Me₅), 94.2 (s, C₅Me₅), 127.2 (SiPh),

127.7 (SiPh), 134.8 (SiPh), 136.2 (SiPh), other signals derived

from phenyl groups were not observed due to the fluxionality

of 2b-a n ti. IR (KBr, cm^-1): 3062, 2978, 2910, 2094 (ν(Ru-

H)), 1965, 1837, 1823, 1739 br (ν(Ru-H-Si)), 1427, 1379, 1228,

1091, 1029, 785, 735, 698, 673. FD-MS: m/e 718. The field

desorption mass spectrum was measured, and the intensities

of the obtained isotopic peaks for C₃₄H₅₀Ru₂Si₂agreed with

the calculated value within experimental error. Anal. Calcd

for C₃₄H₅₀Ru₂Si₂: C, 56.95; H, 7.03. Found: C, 57.53; H, 6.91.

Rea ction of {Cp *Ru (µ-H)}₂(µ-SiMe₂)(µ-SiP h Me) (3c)

w ith H₂. Toluene (10 mL) and the crude product of the

reaction of 1 with PhMe₂SiH (0.0994 g), which included

{Cp*Ru(µ-H)}(µ-SiMe₂)(µ-SiPhMe) (3c) in 80% yield, were

charged in a 50 mL reaction flask. After the reaction vessel

was degassed, 1 atm of H₂was introduced into the flask. The

solution was vigorously stirred for 2 h at 25 °C. The solvent

was then removed at reduced pressure, and a brownish

residual solid including the bis(µ-silyl) complex (Cp*Ru)₂(µ-

η²-HSiMe₂)(µ-η²-HSiPhMe)(µ-H)(H) (2c) in 80% yield was

obtained (0.1040 g). Isolation of 2c by the use of column

chromatography failed due to decomposition on alumina; thus,

formation of 2c was confirmed on the basis of ¹H NMR spectral

data of the crude product. ¹H NMR (400 MHz, 23 °C, THF-

d₈): δ -13.59 (br, 4H, RuH and RuHSi), 0.15 (br, 3H, SiMe₂),

0.41 (br, 3H, SiMe₂), 0.60 (s, 3H, SiMePh), 2.02 (br, 30H, Cp*),

1

7.0-7.5 (m, 5H, SiMePh). H NMR (400 MHz, -95 °C, THF-

2

d₈): δ -15.22 (s, 1H, RuH), -13.50 (s, J _Si-H) 44 Hz, 1H,

2

RuHSi), -13.16 (s, J _Si-H) 44 Hz, 1H, RuHSi), 12.59 (s, 1H,

RuH), 0.18 (s, 3H, SiMe₂), 0.37 (s, 3H, SiMe₂), 0.58 (s, 3H,

SiMePh), 1.97 (s, 15H, Cp*), 2.04 (s, 15H, Cp*), 7.1-7.5 (m,

5H, SiMePh).

Rea ction of {Cp *Ru (µ-H)}₂(µ-SiP h ₂) (4a ) w ith H₂. Tolu-

ene (10 mL) and {Cp*Ru(µ-H)}₂(µ-SiPh₂) (4a ; 0.020 g, 0.030

mmol) were charged in a 50 mL glass autoclave. After the

reaction vessel was degassed, 7 atm of H₂was introduced. The

reaction vessel was heated at 100 °C for 24 h. The solvent was

then evaporated under reduced pressure, and 0.018 g of a dark

reddish residual solid including Cp*Ru(µ-H)₄RuCp* (1), {Cp*Ru-

(µ-H)}₃(µ₃-H)₂, and (Cp*Ru)₄(H)₆was obtained. The ratio

among them was estimated as 32:65:3 on the basis of ¹H NMR

spectra. ¹H NMR (400 MHz, 23 °C, benzene-d₆): Cp*Ru(µ-

H)₄RuCp* (1), δ -13.98 (s, 4H, RuH), 1.87 (s, 30H, Cp*);

{Cp*Ru(µ-H)}₃(µ₃-H)₂, δ -7.24 (s, 5H, RuH), 2.03 (s, 45H, Cp*);

(Cp*Ru)₄(H)₆, δ -9.32 (s, 6H, RuH), 1.90 (s, 60H, Cp*).

P r ep a r a tion of {Cp *Ru (µ-SiP h ₂)(CO)}₂(cis-6a ). Toluene

(10 mL) and {Cp*Ru(µ-SiPh₂)(µ-H)}₂(3a ; 32.0 mg, 0.038 mmol)

P r ep a r a tion of {Cp *Ru (CO)}(µ-SiP h ₂)(µ-CO) (8a ). Tolu-

ene (10 mL) and {Cp*Ru(µ-H)}₂(µ-SiPh₂) (4a ; 0.074 g, 0.11

mmol) were charged in a glass autoclave with 8 atm of carbon

monoxide. The solution was stirred for 6 h at 100 °C. The color

of the solution turned bright yellow from dark red. Removal

of the solvent under reduced pressure afforded a yellow

residual solid containing 8a and {Cp*Ru(CO)(µ-CO)}₂(7) in

3876 Organometallics, Vol. 22, No. 19, 2003

Takao et al.

the ratio of 10:3. The product was dissolved in 4 mL of toluene

and purified by the use of column chromatography on neutral

alumina (Merck Art. 1097) with hexane/toluene. Removal of

the solvent in vacuo afforded 8a as a yellow solid (0.044 g,

54% yield). Recrystallization of the crude mixture from the cold

pentane solution afforded a mixed crystal including 8a and 7

(C₅Me₅), 10.4 (C₅Me₅), 12.0 (SiEt), 20.6 (SiEt), 100.1 (C₅Me₅),

100.3 (C₅Me₅), 127.8 (SiPh), 128.9 (SiPh), 136.4 (SiPh), 147.9

(SiPh-ipso), 204.1 (CO), 204.4 (CO), 262.1 (µ-CO). ²⁹Si{¹H}

NMR (54 MHz, 23 °C, benzene-d₆): δ 216.2. IR (KBr, cm^-1):

3066, 2958, 2902, 2870, 1910 (ν(CO)), 1767 (ν(µ-CO)), 1481,

1427, 1381, 1261, 1093, 1069, 1031, 696. Anal. Calcd for

1

in the ratio of 2:1. H NMR (300 MHz, 23 °C, benzene-d₆): δ

C

₃₁H₄₀O₃Ru₂Si: C, 53.89; H, 5.84. Found: C, 54.19; H, 6.17.

1.63 (s, 30H, Cp*), 7.2-8.0 (m, 10H, SiPh). ¹³C{¹H} NMR (76

MHz, 23 °C, benzene-d₆): δ 9.8 (C₅Me₅), 100.3 (C₅Me₅), 127.5

(SiPh), 128.9 (SiPh), 138.3 (SiPh), 150.1 (SiPh-ipso), 205.3

(CO), 260.3 (µ-CO). ²⁹Si{¹H} NMR (54 MHz, 23 °C, benzene-

d₆): δ 210.7. IR (KBr, cm^-1): 3054, 2988, 2962, 2912, 1916

(ν(CO)), 1754 (ν(µ-CO)), 1481, 1427, 1381, 1085, 1031, 841, 702,

642. FD-MS: m/e 740. The field desorption mass spectrum was

measured, and the intensities of the obtained isotopic peaks

for C₃₅H₄₀O₃Ru₂Si agreed with the calculated value within

experimental error.

P r ep a r a tion of {Cp *Ru (µ-SiP h Me)}₂(P Me₃)(dCdCH₂)

(10). Toluene (10 mL) and {Cp*Ru(µ-SiPhMe)}₂(PMe₃)(H)₂(5;

0.209 g, 0.26 mmol) were charged in a 50 mL flask with 1 atm

of acetylene. The solution was stirred for 2 days at 25 °C.

Removal of the solvent under reduced pressure afforded 0.193

g of a brown solid including 10 in 80% yield (based on ¹H

NMR). Analytically pure 10 was obtained by recrystallization

from cold pentane solution. ¹H NMR (500 MHz, 23 °C, benzene-

d₆): δ 0.96 (s, 6H, SiMe), 1.35 (d, J _H-P) 1.3 Hz, 15H, Cp*),

1.37 (d, J _H-P) 8.0 Hz, 9H, PMe), 1.74 (s, 15H, Cp*), 3.25 (s,

2H, dCdCH₂), 7.2-7.8 (m, 10H, SiPh). ¹³C NMR (68 MHz, 23

°C, benzene-d₆): δ 11.07 (q, J _C-H) 126.8 Hz, C₅Me₅), 11.09

(q, J _C-H) 126.8 Hz, C₅Me₅), 18.0 (dq, J _C-H) 119.2 Hz, J _P-C

) 5.7 Hz, SiMe), 24.3 (dq, J _C-H) 128.8 Hz, J _P-C) 27.7 Hz,

PMe), 91.4 (t, J _C-H) 160.2 Hz, dCdCH₂), 94.2 (s, C₅Me₅), 98.4

(s, C₅Me₅), 126.7 (SiPh), 127.2 (SiPh), 136.1 (SiPh), 153.0

(SiPh-ipso). ²⁹Si{¹H} NMR (54 MHz, 23 °C, benzene-d₆): δ

213.1 (d, J _P-Si) 19.2 Hz). IR (KBr, cm^-1): 3048, 2960, 2898,

1593 (ν(dCdC)), 1474, 1425, 1376, 1300, 1279, 1260, 1227,

P r ep a r a t ion of {Cp *R u (CO)}(µ-SiMeE t )(µ-CO) (8b ).

Toluene (10 mL) and {Cp*Ru(µ-H)}₂(µ-SiMeEt) (4b; 0.074 g,

0.14 mmol) were charged in a glass autoclave with 8 atm of

carbon monoxide. The solution was stirred for 13 h at 110 °C.

The color of the solution turned bright yellow from dark red.

Removal of the solvent under reduced pressure afforded a

yellow residual solid, and the product was dissolved in 4 mL

of toluene. The products was dissolved in 4 mL of pentane and

purified by the use of column chromatography on neutral

alumina (Merck Art. 1097) with hexane/toluene. Removal of

the solvent in vacuo afforded 8b as a yellow solid (0.015 g,

1083, 1026, 945, 782, 732, 710, 650. Anal. Calcd for C₃₉H₅₇

-

PRu₂Si₂: C, 57.46; H, 7.05. Found: C, 57.67; H, 7.39.

1

17% yield). H NMR (300 MHz, 23 °C, benzene-d₆): δ 1.23 (s,

3H, SiMe), 1.49 (t, 3H, J _H-H) 7.2 Hz, SiCH₂CH₃), 1.77 (s, 15H,

Cp*), 1.79 (s, 15H, Cp*), 1.82 (q, J _H-H) 7.2 Hz, SiCH₂CH₃).

P r ep a r a t ion of {Cp *R u (CO)}(µ-SiP h E t )(µ-CO) (8c).

Toluene (10 mL) and {Cp*Ru(µ-H)}₂(µ-SiPh₂) (4a ; 0.070 g, 0.10

mmol) were charged in a glass autoclave with 8 atm of carbon

monoxide. The solution was stirred for 4 h at 110 °C. The color

of the solution turned bright yellow from dark red. Removal

of the solvent under reduced pressure afforded a yellow

residual solid. The product was dissolved in 4 mL of toluene

and purified by the use of column chromatography on neutral

alumina (Merck Art. 1097) with hexane/toluene. Removal of

the solvent in vacuo afforded 8c as a yellow solid (0.025 g,

Ack n ow led gm en t. This research was partly sup-

ported by fellowships of the J apan Society for the

Promotion of Science for J apanese J unior Scientists. We

thank Dr. Masako Tanaka for assistance with the X-ray

structure determination. We also acknowledge Kanto

Chemical Co., Inc., for generous gifts of pentamethyl-

cyclopentadiene.

Su p p or tin g In for m a tion Ava ila ble: Details of the simu-

lation for the VT-NMR studies of 3b-syn and 3c and X-ray

crystallographic data for 3c, 4a ,b, 5, and 8a ,c; X-ray data are

also available as electronic CIF files. This material is available

free of charge via the Internet at http://pubs.acs.org.

1

24% yield). H NMR (300 MHz, 23 °C, benzene-d₆): δ 1.55 (t,

3H, J _H-H) 7.7 Hz, SiCH₂CH₃), 1.64 (s, 15H, Cp*), 1.80 (s,

15H, Cp*), 1.94 (q, J _H-H) 7.7 Hz, SiCH₂CH₃), 7.2-8.1 (m,

5H, SiPh). ¹³C{¹H} NMR (76 MHz, 23 °C, benzene-d₆): δ 9.9

OM030429+

Article Doi

Successive Si-H/Si-C bond cleavage of tertiary silanes on diruthenium centers. Reactivities and fluxional behavior of the bis(μ-silylene) complexes containing μ-hydride ligands

DOI: 10.1021/om030429+

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Article abstract of DOI:10.1021/om030429+

Full text of DOI:10.1021/om030429+

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